Auxiliary verbs are those which are used in the conjugation of other verbs. The English auxiliary verbs are:

• In the present time
  • do
  • be
  • have
  • shall
  • will
  • may
  • can
  • must
• In the past time
  • did
  • was
  • had
  • should
  • would
  • might
  • could

The auxiliaries were originally principal verbs, and some of them are still used as such.
Auxiliary verbs are used to form the modes and tenses of other verbs
and to give to the forms in which they are used the shades of meaning peculiar to their original signification.

For example

go
can read
must sing

Finally, the subordinate infinitive has come to be regarded as the principal verb, and that on which it depended became its auxiliary. The auxiliaries should be regarded as relation words. The auxiliary words are used to show relations of time and mode just as prepositions are used to show relations of time, place, origin, cause, manner, property, or material. In fact, all words used to show a relation of whatever nature, such as prepositions, relative pronouns, and conjunctive adverbs, are auxiliary words.
In the progress of the development of the English language, all auxiliaries have increased; and inflectional changes of the principal word have diminished. An exact and familiar acquaintance with the various uses of the auxiliary verbs is essential to the understanding of the English language.
The auxiliary verbs, as verbs, have only two tenses, present and past.  As an exception, the auxiliary verb must has no tense variation.

Auxiliary verbs and their tense forms are represented in the following conjugation tables:

Present Tense Conjugation of Auxiliary Verbs

	Singular			Plural
I	you	he, she, it	we	you	they
am	are	is	are	are	are
do	do	does	do	do	do
have	have	has	have	have	have

In the present tense, the auxiliary verbs will, shall. may, can, and must have a single form for all persons and numbers.

Past Tense Conjugation of Auxiliary Verbs

	Singular			Plural
I	you	he, she, it	we	you	they
was	were	was	were	were	were

In the past tense, the auxiliary verbs did, have, would, should, might, can and could have a single form for all persons and numbers.

The Meaning of the Auxiliaries

The auxiliaries, deriving much of their force from their original meaning. Each gives its own shades of meaning to the tense form in which it is used.
Be comes from the Saxon beon which meant to be fixed or to exist. The use of the auxiliary be in any of its forms denotes existence.

As auxiliaries, forms of the linking verb (also called the copula), to be join an attribute and assert its existence in a subject.

For example

The heat is oppressive.

Do comes from the Saxon don meaning to do. The use of the auxiliary do in any of its forms denotes action.
As an auxiliary, do is used chiefly to give intensity of meaning to the action of a principal verb. This it does especially in affirmative sentences, and, to some degree, in negative sentences. In interrogative sentences, do is little more than a sign of interrogation.

For example

I do try.
I did go.
He did not speak.
Do you hear it?

Have comes from the Saxon habban meaning to have or to complete. The use of the auxiliary have in any of its forms denotes possession.
As an auxiliary, have retains its original meaning of completion as if an act was not fully possessed by its subject until completed.

For example

In the sentence
I have treasures concealed.
have denotes possession, and it is separated from concealed. In this sentence, it is the treasures that are possessed.

In the sentence
I have concealed treasures.
have still denotes possession, but is brought into connection with concealed. This sentence has two possible meanings. In one, it is the act of concealing that is possessed. In the other it is the treasures that happen to be concealed that is possessed.

In the sentence
I have concealed the treasures.
have is brought into intimate relation with concealed, and passes from a passive to an active signification. This sentence suggests that the idea of possession of an act is in the completion of the act.
Shall comes from the Saxon scealan meaning to be obliged. Will comes from the Saxon willan meaning to determine.
Shall and will as auxiliaries have a complex signification when a future event is made to depend upon the determination, resolution, or volition of a personal agent, either the actor or another.

For example

He shall go (I so resolve).
I will go (I, myself, so resolve).

Will and shall in its simple signification denotes mere futurity. When used, the future event is wholly or chiefly independent of volition or resolution.

For example

It will rain (whatever you or I may resolve).
I shall be overtaken (independent of my will).

In these cases the speaker merely predicts or expresses an opinion.
The past tenses should and would are used with the same or nearly the same significations.
The following rules apply to shall and will.

• When the person who resolves or predicts the action is not mentioned, the speaker or first person is understood in affirmative sentences. The hearer or second person is understood in interrogative sentences.

For example

You shall go. (I will it.)
Shall he go? (Do you will it?)
It will rain, (I predict it.)
Will it rain? (Do you predict it?)

• In older forms of English and in the most formal of current usage, will should be used when the resolution and the action are attributed to the same person, and shall when they are attributed to different persons.

For example

I will go. (I myself resolve.)
Will you go? (Do you yourself resolve?)
He will go. (He himself resolves.)
He shall go. (I resolve.)
They have determined that you shall go.
Shall he go? (Do you resolve?)

• In very formal usage, shall should be used when the prediction and the action are both attributed to the same person, or in any case, provided the action be attributed to the first person. Will should be used when the prediction and the action, except in the case of the first person, are attributed to different persons.

For example

You will be promoted. (I predict it.)
I shall teach, or be a teacher. (I, he, you, or they, predict it.)
Will he teach? (Do you predict it?)
Will it rain? (Do you think so?)
It will rain. (I think so.)

• Shall is used in animated discourse, contrary to the last part of the third rule, when the speaker offers an implied pledge that his prediction shall be fulfilled.

For example

When the precepts of the gospel shall have been thoroughly inwrought
into the lives of men, then shall war be known only in history.
I shall return.

May comes from the Saxon magnn meaning to be strong. The Saxon word expressed the primary idea of power, and implied a personal agency from without employed to remove all hindrance; hence, it suggested the idea of permission.
Can comes from the Saxon cunnan meaning to know. The Saxon word suggests an intelectual power within one’s self, and, hence, the idea of ability.
Must comes from the Saxon motan meaning to be able. The Saxon word suggests being impelled by a power coming, not from any personal agency without, as in case of may, nor within, as in case of can, but from the nature, constitution, or fitness of things. Hence, we have the idea of necessity, and, in a moral point of view, obligation.

Note

Since may, can, and must agree in the idea of power, they all suggest potential. They differ in the source of the power or potential. As auxiliaries, they retain much of their original meaning.

May sometimes denotes possibility but implies doubt.

For example

It may rain.
He may have written.

May is also sometimes a petition.

For example

May it please you.

Might and could also express in past time the same general meaning as may and can in the present.

For example

I know I may or can go.
I knew I might or could go.

Might, could, should, and would are used in conditional sentences. Might in one clause can answer to could in the other when power, ability, or inclination is implied.

For example

He might sing, if he could or would.
He could sing, if he would.
He would sing, if he could.

Sometimes the conditional clause is omitted.

For example

He might write.
He could write.
He would write.

In all these examples, a present possibility or liberty is referred to. When past time is referred to, we use the past perfect tense.

For example

He might have written, if he would (have written).

At this point proceed to Exercise 23.