Common errors in the uses of modal verbs may, might made by the students in the grade 11 at que vo high school

HANOI PEDAGOGICAL UNIVERSITY N0. 2
FOREIGN LANGUAGE FACULTY

NGUYEN THI LAM

COMMON ERRORS IN THE USES OF MODAL VERBS
“CAN”, “COULD”, “MAY”, “MIGHT”
MADE BY THE STUDENTS IN THE GRADE 11
AT QUE VO HIGH SCHOOL
(SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS OF THE
DEGREE OF BACHELOR OF ARTS IN ENGLISH)

Supervisor: NGUYEN VAN DEN, M.A

Hanoi, 2013
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ACKNOWLEDGEMENTS

First of all, I would like to express my respect and my deepest thanks to my
supervisor Mr. Nguyen Van Den, M.A - Dean of English Faculty, Hanoi
Pedagogical University No 2 for his enthusiastic guidance, warm encouragement
and useful research experiences.
I am greatly indebted to the teachers of English at Que Vo 2 High School,
especially Mrs. Duong Thi Hoi for her help and guidance while I was carrying out
the survey.
I wish to gratefully thank all the teachers of Hanoi Pedagogical University
No 2 for their invaluable knowledge which they provide me during the past four
academic years.
I would also like to send my special thanks to my friends in K35A class, for

their enthusiasm and kindness in helping me collect valuable reference documents
and data for my research.
Last, but not least, my family is really the biggest motivation for me. My
parents and my brother always encourage me when I have stress and difficulty. I
would like to send them great love and gratefulness.

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ABSTRACT

The modal verb is an interesting category of English grammar. There is
category that always poses a question to me. It is a particular kind of auxiliary.
However, the uses of the modals “can”, “could”, “may”, “might” referred to in
some books have not been dealt with in full and sometimes cause confusion to
learners of English.
As a result, students of English often make errors when they use the modals
“can”, “could”, “may”, “might”. Therefore, this research work entails studying the
uses of them and conducting a survey for error analysis.
Base on the result of the survey, the types of errors and causes have been
found. Solutions to the problems have been suggested.

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STATEMENT OF AUTHORSHIP

Title: Common Errors in the Uses of modal verbs “can”, “could”, “may”,
“might” made by the students in the grade 11 at Que Vo High School
(Graduation paper submitted in partial fulfillment of the Degree of Bachelor of

Arts in English)

I certify that no part of this report has been copied or reproduced by me from
any other person’s work without acknowledgements and that the report is
originally written by me under strict guidance from my supervisor.

Date submitted: May 2013
Student

Supervisor

Nguyen Thi Lam

Nguyen Van Den, M.A.

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TABLE OF CONTENTS

Acknowledgement ................................................................................................ ii
Abstract ............................................................................................................... iii
Statement of authorship ...................................................................................... iv
Table of contents .................................................................................................. v

PART ONE
INTRODUCTION

I. Rationale ........................................................................................................... 1
II. Research presupposition ................................................................................. 2

III. Research objectives........................................................................................ 2
IV. Research scope ............................................................................................... 2
V. Research tasks ................................................................................................. 3
VI. Research methods .......................................................................................... 3
VII. Significance of the proposed research ......................................................... 3
VIII. Design of the research work ....................................................................... 4

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PART TWO
DEVELOPMENT
CHAPTER ONE: THEORETICAL BACKGROUND
I.1. Literature review in brief ............................................................................... 5
I.2. “Can”, “could”, “may” and “might” ............................................................ 6
I.2.1. “Can”, “could”, “may” and “might” as modality ...................................... 6
I.2.1.1. Definition ................................................................................................... 6
I.2.1.2. Classification.............................................................................................. 7
I.2.1.3. Epistemic and deontic modals “can”, “could” “may”, “might”................... 7
I.2.2. Some Grammatical Features of “can”, “could”, “may” and “might” ..... 8
I.2.2.1. Forms of “can”, “could”, “may” and “might”............................................. 9
I.2.2.1.1. Positive form ........................................................................................... 9
I.2.2.1.2. Negative form ....................................................................................... 10
I.2.2.1.3. Interrogative form ................................................................................. 11
I.2.2.2 Tenses of “can”, “could”, “may” and “might” ........................................... 11
I.2.2.2.1. Present tense.......................................................................................... 11
I.2.2.2.2. Past tense............................................................................................... 12
I.2.2.3. “Can”, “could”, “may” and “might” combined with aspect and voice ...... 12
I.2.2.3.1. “Can”, “could”, “may” and “might” with perfect aspect ........................ 12
I.2.2.3.2. “Can”, “could”, “may” and “might” with progressive aspect................. 12

I.2.2.3.3. “Can”, “could”, “may” and “might” with passive voice ........................ 12
I.2.3 Meaning/ uses of “can”, “could”, “may” and “might” ............................ 13
I.2.4.1. Possibility ................................................................................................ 13
I.2.4.2. Ability ...................................................................................................... 15
I.2.4.3. Permission................................................................................................ 17
I.2.4.4. Request .................................................................................................... 18

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CHAPTER TWO: COMMON ERRORS IN THE USE OF THE MODAL
VERBS “CAN”, “COULD, “MAY”, “MIGHT”

II.1. Survey ......................................................................................................... 19
II.1.1. Purpose of the survey ................................................................................. 19
II.1.2. Population of the survey ............................................................................ 19
II.1.3. Type of the survey ..................................................................................... 20
II.1.4. Construction of the test .............................................................................. 20
II.1.5. Preparation of the survey ........................................................................... 20
II.1.5.1. Test items................................................................................................ 20
II.1.5.2. Arrangement of the test items ................................................................. 21
II.1.6. Administration of the try-out ..................................................................... 22
II.1.6.1. Preparation of the try-out ........................................................................ 22
II.1.6.2. Try-out .................................................................................................... 22
II.1.7. Method of data analysis ............................................................................. 23
II.1.8. Results of the survey .................................................................................. 23
II.2. Common errors and causes........................................................................ 25
II.2.1. Errors in the wrong verb use “can”, “could”, “may”, “might .............. 25
II.2.1.1. Errors in the use of “can, “could” vs “may”, “might”.............................. 26
II.2.1.2. Errors in the use of “can”, “could” vs “be able to”, “be allowed to”........ 26

II.2.1.3. Errors in the use of “may”, “might” and “be able to”, “be allowed to” .... 26
II.2.2. Errors in the wrong tense use “can”, “could”, “may”, “might”… ....... 27
II.2.2.1. Errors in the use of the modal verbs with perfect aspect ......................... 27
II.2.2.2. Errors in the use of the modal verbs with progressive aspect................... 27
II.2.2.3. Errors in the use of the modal verbs with the present/ future ................... 27
II.2.2.4. Errors in the use of the modal verbs with the past ................................... 28
II.2.3. Errors in the use of “can”, “could”, “may”, “might” in sentences ....... 28
II.2.3.1. Errors in the use of “can”, “could”, “may”, “might” in passive voice...... 28
II.2.3.2. Errors in the use of “can”, “could”, “may”, “might” in reported speech. . 28

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II.2.3.3. Errors in the use of “can”, “could”, “may”, “might” in conditional
sentences .............................................................................................................. 29
II.2.3.4. Errors in the use of “can”, “could”, “may”, “might” in wishing
sentences .............................................................................................................. 29
II.2.4. Errors in the addition .............................................................................. 29
II.2.4.1. Errors in the addition of -S, -ES .............................................................. 29
II.2.4.2 Errors in the addition of TO ..................................................................... 30
II.2.4.3. Errors in the addition of another modal verb ........................................... 30
II.3. Suggested and solutions ............................................................................. 30
II.3.1. Suggested solutions.................................................................................... 30
II.3.2. Suggested exercises ................................................................................... 31

PART THREE
CONCLUSION

CONCLUSION................................................................................................... 33
REFERENCES ................................................................................................... 35

APPENDICES .................................................................................................... 37
SURVEY QUESTIONNAIRE ............................................................................. 37
SUGGESTED EXERCISES ................................................................................ 44

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PART ONE
INTRODUCTION

I. Rationale
Nowadays, English is the most widely used in the world and plays an
important role in the development of society and technology. It is the bridge
connecting countries in many fields. The mastery of foreign language enables us to
communicate with people from other countries, achieve mutual understandings,
and further our trade contacts, economic co-operations, and cultural and academic
exchanges with other countries.
In Vietnam, English is the compulsory subject for pupils in most of schools.
It is also an important subject for students at all universities. Particularly, English
is one of the essential requirements for those who want to find a good job.
However it is not simple. We have to pay attention to grammar, structure,
vocabulary, and pronunciation. It is easy to make mistakes and often find a lot of
difficulties in using the modal verbs when dealing with grammar. It is proved that
English grammar is complex and often causes embarrassment to students. The
modal verbs are one of the language categories that students at high school have to
learn much. Due to its various uses, it is assumed that are many errors which may
be made. In fact, many students confess that the modal verbs is one of the biggest
problems of English grammar and often make errors in the use of the modals,
especially modal verbs “can”, “could”, “may”, “might”. For examples:
She cans sing well.

We don't may go to the party tomorrow.
Moreover, as a prospective teacher, I would like to make a contribution to
the English teaching in Vietnam. For the reasons above, I conducted, which focus
on errors in the uses of modal verbs “can”, “could”, “may”, “might” among the
students of English in grade 11 at Que Vo 2 High School.

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II. Research presupposition
Some questions are raised:
1) What kinds of errors in using the modal verbs “can”, “could”, “may”,
“might” are made by the students of English in grade 11 at Que Vo 2 High School
in the school year of 2012/2013?
2) What are the causes of the errors in the uses of the modal verbs “can”,
“could”, “may”, “might” made by the students of English in grade 11 at Que Vo 2
School in the school year of 2012/2013?
3) What are some effective ways that help the students of English in grade
11 at Que Vo 2 High School in the school year of 2012/2013 overcome these
difficulties in the uses of the modal verbs “can”, “could”, “may”, “might”?
III. Research objectives
The study is aimed at the following goals:
1) To find out the kinds of errors made by the eleventh -grade students of
English Que Vo 2 High School in the school year of 2012/2013 in using the modal
verbs “can”, “could”, “may”, “might”.
2) To find out the causes of the errors in the uses of the modal verbs “can”,
“could”, “may”, “might” made by the students of English in grade 11 at Que Vo 2
School in the school year of 2012/2013.
3) To find the best solutions to the problems throughout the survey. The
solutions might be concentrated on both theory and practice, in which some

teaching techniques are also introduced with the goal of minimizing students’
errors at Que Vo 2 High School.
IV. Research scope
The general research area of this study is grammar. The phenomenon is
errors in the uses of the modal verbs “can”, “could”, “may”, “might” made by the
students of English in grade 11 at Que Vo 2 High School in the school year of
2012/2013. Others relating to the definite preposition of purpose are also brief
mentioned.

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The population involved in the study is one hundred eleventh -grade
students of English (11A5, 11A6) at Que Vo 2 High School.
V. Research tasks
The study involves fulfilling the following tasks:
1) To study the definition and classification of the modality.
2) To research into the grammatical features and uses of the modal verbs
“can”, “could”, “may”, “might”.
3) To conduct a survey to find out error types and causes of modal verbs
“can”, “could”, “may”, “might” in English. On the basis of the findings, possible
solutions to the problems are found to minimize the students’ errors.
VI. Research methods
To achieve the objectives of the study, the following methods have been
applied:
1) Collecting documents from books listed in the references
2) Consulting the supervisor, experienced teachers and friends
3) Synthesizing theoretical documents on English grammar
4) Conducting a survey and analyzing the results
5) Interviewing some typical students

VII. Significance of the proposed research
Errors in any language teaching and learning, particularly in English as a
foreign language, are sometimes predictable and sometimes unpredictable. It is,
therefore, essential for teachers to have better treatment to anticipate errors. After
the research, it is hoped that the results will be helpful to provide:
1) Input for learners of English in order to minimize their errors in the uses
of the modal verbs “can”, “could”, “may”, “might” in English.
2) Input for teachers of English with information on error types and
solutions to the problems so that they can have good methods of teaching the
modal verbs “can”, “could”, “may”, “might” in English.
This study is also beneficial to anyone who is interested in the modal verbs
“can”, “could”, “may”, “might” in English.
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VIII. Design of the research work
The research work has three main parts, namely: Introduction, Development,
and Conclusion. The development consists two chapters. Chapter one is entitled
“Theoretical Background”. It consists two sections. Section one reviews literature
in brief. The second one deals with things related to the definition, classification,
grammatical features and uses of the modal verbs “can”, “could”, “may”, “might”
in English.
Chapter two is named “Common errors in the uses of the modal verbs “can”,
“could”, “may”, “might””. It has three sections. Section one is devoted to the
survey. The second deals with error types and causes. The last one is on solutions
to the problems and suggested exercises.

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PART TWO
DEVELOPMENT

CHAPTER ONE: THEORETICAL BACKGROUND

I.1. Literature review in brief
In English language, modal verbs, especially “can”, “could”, “may”,
“might” has been described many grammarians like Aik and Hui (1992) in the
book Longman Dictionary of Grammar and Usage, Estwood (1994) in the book
Oxford Guide to English Grammar, Jacobs (1995) in A Grammar for English
Language Professional, Hewings (1999) in Advanced Grammar in Use, Murphy
(2000) in the book English Grammar in Use, Palmer (1974) in The English Verb,
Quirk et al (1985) in A Comprehensive Grammar of the English Language, etc.
They have their own way to describe the modal verbs “can”, “could”, “may”,
“might”. Generally, they focus on the definition, characteristic, classification,
functions and the uses of them.
Aik and Hui (1992) in the book Longman Dictionary of Grammar and
Usage give a definition of modal verbs. They mention the function as well as
structure of them. Besides, they point out some errors in the use and misuse of
modal verbs “can”, “could”, “may”, “might”.
Estwood( 1994) in the book Oxford Guide to English Grammar only focuses
on his attention to structure and gives examples of modal verbs “can”, “could”,
“may”, “might”.
Jacobs (1995) in A Grammar for English Language Professional refers to
the forms, types of modal verbs “can”, “could”, “may”, “might” in English. It deals
with possibility or probability, ability, request.
Hewings ( 1999) in Advanced Grammar in Use gives us the uses of modal
verbs “can”, “could”, “may”, “might” which are presented clearly with
explanations and examples.

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Murphy (2000) in the book English Grammar in Use, focuses on the
definition, form and uses of the modal verbs “can”, “could”, “may”, “might”.
Quirk et al. (1985) in A Comprehensive Grammar of the English Language
agree in studying modal verbs “can”, “could”, “may”, “might” by giving each
modal the meanings of the modal necessity, possibility, ability and permission etc.
Palmer (1974) in T he English Verb focus on two broad clusters of meaning:
Epistemic modal meanings which dealt with the degree of speaker
commitment that forms the complement of the modals. Deontic modal meanings
concerned with the necessity, possibility, obligation and permission.
In short, many researches have been done the modal verbs “can”, “could”,
“may”, “might” but only Aik and Hui (1992) points out errors in the use of them.
In fact, there are more far more errors that learners of English often make when
they use them. Therefore, it is essential to have a comprehensive study of common
errors in the use of “can”, “could”, “may”, “might”.
I.2. “Can”, “could”, “may” and “might”
I.2.1. “Can”, “could”, “may” and “might” as modality
I.2.1.1. Definition
There are many definition of modality written by a number of linguists.
Palmer F.R (1986) defined modality as “Modality expresses the attitude and
opinion of the speaker toward the representational content of the sentence”.
“Modality is understood as a very wide category inherent in any sentence
and showing the relation between the statements affirmed the sentence and reality
as establish by the speaker”.
“Modality is the grammaticalized expression of the subjective attitudes and
opinions of the speaker including possibility, probability, necessity, obligation,
permissibility, ability, desire, and contingency”.
In the study of modality, we should not only consider the ways speaker

express their attitudes and opinions but also the ways in which others may report
their expressions of them. For examples:

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He may be there.
He thought he was there.
In my opinion, modality can indicate the degree of commitment of the
speaker. Moreover, the speaker can participate by defining in some ways under
what condition he is speaking.
English modal verbs are used to express the speaker’s attitudes or opinions
like judgment, assessment or intention. From semantic functions, they can denote
epistemic and deontic meanings.
I.2.1.2. Classification
* Epistemic modality
Epistemic modals are used to indicate necessity, probability, possibility or
judgment. Epistemic modals refer to the speaker’s knowledge, judgment, or belief
about the events, affairs or actions. They bind the speaker to commit to the
proposition whether it is true or not in the real world. Examples of the expression
of epistemic modality in English are:
He might be there (low probability, substantial doubt)
He may be there (possibility)
* Deontic modality
Deontic modals (root modals) express obligation, permission, intention, and
ability (Greenbaum, 1991, p.97). Deontic modality is concerned with “influencing
actions, states, or events”. They bind the speaker to lay an obligation, give
permission or prohibition. They also reflect the subject’s ability (Azar, 1995, p.55;
Palmer, 1990, p.5-8; Sweetser, 1990, p.49-51). Look at these examples:
She can go (ability)

You may go (permission)
I.2.1.3 Epistemic and deontic modals “can”, “could”, “may”, “might”.
The modals “can”, “could” “may”, “might” discussed in this study can be
used epistemically or deontically at the same time. Groefsema (1995, p.53) notes
that “these modals can often be interpreted either epistemically or deontically”. As
in the example: “John may leave tonight”, there are two different interpretations.
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One is that, “It’s possible that John leaves tonight.” The other is that, “John is
permitted to leave tonight”. The two interpretations represent epistemic possibility
and deontic permission respectively.
Epistemic meanings of modal verbs are related to the speaker’s subjective
interpretation of the real world situation, which can be roughly divided into three
categories: necessity, prediction and possibility. Epistemic necessity indicates the
speaker’s certainty about the proposition. The group modal verbs of “can”, “could”
“may”, “might” are used to show epistemic possibility, which indicates the
different levels of the speaker’s uncertainty about the proposition (Jackson, 1990,
p.99-101; Quirk et al, 1985, p.219-31).
Deontic modal verbs are associated with real world. By using them, the
speaker may lay an obligation, give permission, and show his volition and ability.
The modal verbs “can”, “could” “may”, “might” belong to deontic permission. To
get a clearer understanding on the usage of each modal verb in different meanings,
please see Table 1:

Modal
Verbs
CAN

COULD

MAY

MIGHT

Epistemic

Deontic

necessity prediction possibility obligation volition permission ability
×

×

×

×

×

×

×

×

×

×

I.2.2. Some Grammatical Features of “can”, “could”, “may”, “might”
English modal verbs as a part of auxiliary verbs share the following
grammatical characteristics of auxiliary verbs:
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a. They are not inflected in the third person; that is, when the subject is
singular third person, no subject-verb agreement realizes in inflection so the form
should be “He may come” instead of “He mays come”.
b. They are followed by the “bare infinitive” the base form of the verb alone.
In other words, after modal verbs, the infinitive without to of other verbs is
used so the form is “I can swim” but not “I can to swim”.
c. They are negated by the addition of “n’t” or “not”. They are not added to
“don’t” as other verbs. That is, the negation of modal verbs is “I can’t” or “I
cannot” rather than “I don’t can”.
d. They are inverted with the subject to form a question without using “do”.
For example, the interrogative sentence is “Can I do it?” but not “Do I can do it?”
e. They have no non-finite forms—past and present participles.
f. They can’t co-occur. In other words, two modal verbs can’t be used
simultaneously so the correct form is “He may come” or “He will come” instead of
“He may will come” (Palmer, 1990, p.4-5; Walker, 2000, p.121; Quirk, Leech, &
Swan, 1984, p.127-28).
These grammatical characteristics are different from those of the main verbs.
For example, present-tense verbs with third person singular subjects require an –s
ending. Some linguists, such as Vince and Lim, think these differences might give
rise to learning difficulty for students. However, according to my observation,
Vietnamese students seldom get confused choosing correct modal verb forms. It
seems that these grammatical characteristics are not the source of students’
difficulty.
I.2.2.1. Forms of “can”, “could”, “may”, “might”

I.2.2.1.1. Positive form
The positive form in English modality “can”, “could” “may”, “might” are
the following bare verb. For examples:
Anybody can make mistakes.
I never could play the banjo.
You may borrow my car if you like.
We might go to the concert.
(Quirk, 2002, p.52, 53)
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I.2.2.1.2. Negative form
The negation of modal verbs is to add “not” to the sentence. The form of
negation in English modality “can”, “could”, “may”, “might” are very easy- just
put a negative word “not” after the modal verb to form the negation. However, the
meaning of the negative sentence is not as easy as its surface form shows. The
negative sentence does not merely indicate the opposite meaning to the positive
sentence- epistemically or deontically. “Not” in the modality system can mean two
very different things. As Cook (1978, p.7-10) puts it, a sentence with modal verbs
is two verb structures- the modal verb and the main verb. And, it would be a little
complicated when the word “not” is put in the sentence. For the negative can
negate the modal verb called modal negation or negate the main verb called main
verb negation. For example (Leech, 1987, p.91):
(1) He can’t be serious. (Modal negation)
(2) He may not be serious. (Main verb negation)
Example (1) means it is not possible that he is serious so it is the modal verb
that is negated, while example (2) means that it is possible that he is not serious so
it is the main verb that is negated. As mentioned above, the form of the negation of
modal verbs is added to a negative word “not”. Nonetheless, when it comes to the
negation of meaning, there are some exceptions. Look at the following examples

(Cook, 1978, p.8):
(3) John may be lying.
(It’s possible that John is lying. => epistemic possibility)
(4) John may not be lying.
(It’s possible that John is not lying. =>main verb negation)
(5) John can’t be lying.
(It’s not possible that John is lying. =>modal negation)
In example (3), the sentence John may be lying—means that “It’s possible
that John is lying.” The contradictory does not simply add “not” to the sentence
because example (4) John may not be lying means “It’s possible that John is not
lying”. However, example (5) John can’t be lying means “It’s not possible that
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John is lying”. It’s very obvious that the contradictory of “may” in possibility is
can not but not may not.
I.2.2.1.3. Interrogative form
As for interrogation, Palmer (1990, p.41) suggests that “with interrogation,
only the modality, never the proposition, can be questioned.” That is, the modal
verb, which is used to form the negation, is used for interrogation. For examples:
(6) John may still be reading. (epistemic possibility)
(7) John can’t still be reading.
(8) Can John still be reading?
(9) May John be reading? (deontic permission)
In example (6), the sentence John may still be reading means “It is possible
that John is still reading. Its negation does not just add “not” to the sentence, but
changes the modal verb “may” to “can” as is explained above. Therefore, the
contradictory sentence John can’t still be reading as in example (7), which means
“It’s not possible that John is still reading.” Similarly, to form the interrogative
sentence, only can but not may is used. Example (8) Can John still be reading

means “Is it possible that John is still reading”. As Dean (1994, p.54) proposes that
“may used in a question is always deontic, never epistemic”. Hence, example (9)
May John be reading means “Is John permitted to be reading”.
I.2.2.2 Tenses of “can”, “could”, “may” and “might”
The modals “can”, “could” “may”, “might” discussed in the study are used
for the present and past time because the proposition is possibility, permission and
ability by the speaker to happen in the present and past.
I.2.2.2.1. Present tense
The modals “can”, “may” are the present tense form. Look at following
examples:
He can speak English now.
Today we may stay the whole afternoon.
(Quirk, 2002, p.56)

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I.2.2.2.2. Past tense
The modals “could”, “might” are the past tense forms of “can” “may”. These
examples:
Could I borrow your pencil?
It might rain.
(Frank, 1972, p.97)
John could run ten miles with ease, when he was young.
(Palmer, 1990, p.45)
I.2.2.3. “can”, “could”, “may”, “might” combined with aspect and voice
I.2.2.3.1. “can”, “could”, “may”, “might” with perfect aspect
The modals “can”, “could” “may”, “might” with perfect aspect (modal +
have+ ed-participle). For example:
The demand for subject access may have come as a shock to the library

profession. (ACAD)
May and might are used with the perfect to express a certain degree of doubt
about past events or situations. Take the example:
Also he may have had quite a job finding it. (FICT)
Yesterday he confessed he might have forgotten one. (NEWS)
I.2.2.3.2. “can”, “could”, “may” and “might” with progressive aspect
The modals “can”, “could” “may”, “might” with progressive aspect (modal
+ be + ing- participle). Look at this example:
Nancy can be coming back. (CONV)
I.2.2.3.3. “can”, “could”, “may” and “might” with passive voice
The modals “can”, “could”, “may”, “might” with passive voice (modals +
be + ed-participle). For instance:
The door can be locked.
Can and could are relatively common with passive voice. The uses of the
passive avoid identification of the agent of the main verb. As a result, the
permission meaning doesn’t occur, and the ability meaning is also less likely to

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occur than in the active; therefore, the possibility meaning is most common in
passive:
Each interpretation can be seen generally to flow through the abbreviated
text as a whole. (ACAD)
<compare active voice: We can see each interpretation…-ability.>
The methods could be refined and made more accurate. (ACAD)

<compare active voice: We could refine the methods…- ability.>
I.2.3 Meaning/ uses of the modal verbs “can”, “could”, “may”, “might”
I.2.3.1. Possibility “can”, “could”, “may”, “might”

1. Theoretical possibility.
Can is used to say that events and situations are possible (without talking
about the chances of them actually happening).
Anybody can make mistakes
The road can be blocked (=it is possible to block the road)
(Quirk, 2002, p.52)
2. Factual possibility
a. Future possibility
We don't use can to say that there is a chance that something will happen.
Instead, we usually use may or might (without any significant difference in
meaning in modern English).
We may go climbing this summer.
The door might be closed (=it is possible that the door is closed)
Could is used to give the idea that something is just possible. For examples:
We could go to the concert, but I doubt if we'll have time.
It could rain later on this evening.
b. Present possibility
May, might and could are also used to say that something is possibly true at
the moment of speaking.
You may be right.
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You could be right, but I don't think you are.
What you say might be true.
3. May and might with the perfect infinitive.
Both may and might can be used with perfect infinitives to talk about the
possibility that past events happened.
He may/might have gone (=it is possible that he has gone)
(= perhaps he has gone)

He said/ thought that she might have missed the plane.
(Thomson, 1999, p132)
Might can also be used in this structure to say that a past event was possible,
but didn't happen.
You were stupid to try climbing up there. You might have killed yourself.
4. Can and could with the perfect infinitive.
* Can and could are both used with the perfect infinitive for speculating or
guessing about the past.
Can is only used in questions and negative sentences.
Can you get to the top of the mountain in one day?
She could have gone off with some friends. (Not she can have gone...)
* Could with the perfect infinitive is also used (as might was) to talk about
an unrealized past possibility. Something that was possible but didn't happen.
You were stupid to go skiing there - you could have broken your leg.
It wasn't a good idea to throw the TV out of the window - it could have hit
somebody.
This structure can be used to criticize people for not doing things.
You could have told me you had invited people to dinner.
(=Why didn't you tell me ...?)
* To say that something was not a possibility, we say it couldn't have
happened.
My parents wanted me to be a doctor, but I couldn't have put up with all
those years of study.
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I.2.4.2. Ability “can”, “could”
1. Present and future
* Can is usually used to talk bout the present, or about 'general ability' - the
ability to do something any time you want to.

He can speak English but he can’t write very well
(Quirk, 2002, p51)
* To talk about future ability, will be able to is normally used.
I'll be able to speak German in another few months.
Our baby will be able to walk in a few weeks.
(Thomson, 1999, p134)
But can is often possible when people make present decisions about future
ability.
I can’t pay you today. Can you wait till tomorrow?
(Thomson, 1999, p134)
2. Past
* Could is used for 'general ability', to say that you could do something any
time you wanted to.
When I was young I could climb any tree in the forest.
(Thomson, 1999, p135)
* Could is not used to talk about particular ability (to do something on one
occasion) in the past. Instead, we use was able to, managed to, or succeeded in.
How many eggs were you able to get.
I managed to get 10% off the price.
After six hours' climbing, we succeeded in reaching the top of the mountain.
Compare the following two sentences:
He was a terrific liar: he could make anybody believe him. (General ability could is correct.)
I talked for a long time, and in the end I managed to make her believe me.
(One particular action – could is impossible here).

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* Note that the negative couldn't is used for both general and particular
ability.

When I was younger I couldn't decide what I wanted to do.
Simon was so drunk that he couldn't find the front door.
3. Conditional could
Could is also used in a conditional sense (meaning “would be able to”).
I could have a really good time if I had a flat of my own.
We could do it by midday if we had the tools.
4. Could with the perfect infinitive
Sometimes we want to say that we had the ability to do something, but we
didn't try to do it. There is a special structure for this could + perfect infinitive
(=could have + past participle)
I could have married anybody I wanted to. (=I was able to marry anybody...,
but I didn't.)
I could have killed her! (=I was so angry that I was capable of killing her,
but I didn't.)
You could have helped me! (=You were able to help me - why didn't you?)
5. Could in reported speech
* Could for present ability does not change:
“I can’t/couldn’t stand on my head” he said:
= He said he couldn’t stand on his head.
Could for future ability can remain unchanged or be reported by would be
able:
He said: “I could do it tomorrow”
= he said he could/ would be able to do it the next day.
* Could in type 2 conditional sentences is reported similarly:
“If I had the tools I could mend it” he said:
= he said that if he had the tools he could/ would be able to mend it.
* Could in type 3 conditional sentences is reported unchanged.

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* Could for past ability can remain unchanged or be reported by have been
able:
“I could read when I was there!” she boasted:
= She basted that she could/ had been able to read when she was there.
I.2.4.3. Permission “can”, “could”, “may”, “might”
1. Asking for permission.
* Can, could, may and might are all used in asking for permission. Can is
probably the commonest of the four.
Can I have a drop more whisky?
* Could is rather more hesitant that can, and is used when you are not sure
that you will get permission (or when you don't want to sound too sure).
Could I ask you something, if you're not too busy?
* May and might are used in a more formal style; they often suggest respect.
Might is more hesitant, and is not very common.
May I make a suggestion?
May I stop work a little earlier tonight?
Might I take the liberty of pointing out that you have made a small mistake?
Note that, in asking for permission, could and might are not past tenses; all
four words refer to the future.
2. Giving permission.
When we give permission, we use can and may, but not could or might.
Could I use your phone? - Yes, of course you can.
Might I trouble you for a light? - You may indeed.
3. Past permission.
In the past, could is used to say that one was allowed to do something at any
time ('general permission').
When I lived at home, I could watch TV whenever I wanted to.
But we don't use could to talk about permission for one particular action in
the past. Look at these examples:

I was allowed to see her yesterday evening.
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