Difference between auxiliary and main verb

(Particularities of the two verb types in English)

What is the difference between an English auxiliary and a main verb?

Also in English grammar, the distinction between auxiliary verb and full or main verb is very important. Both types have different functions in a sentence (which implies that they have different tasks) and consequently cannot ‘substitute’ or replace each other.

This differentiation plays a significant role in terms of grammar in order to be able to form a correct sentence. The following applies:

In English, only these three auxiliary verbs exist:
- be, do, have
  - Information: Modal verbs (‘may, can, could, must’, etc.) also belong to the group of auxiliary verbs but have special rules in their use.
  - Function: They serve, among other things, to form the compound tenses, the progressive forms, the passive voice, as well as negations and questions.
Full verbs, on the other hand, are all remaining verbs. Therefore, they are unlimited in their number. Examples are:
- to go, dance, know, evacuate, fly, repair, etc.
  - Be careful: The three auxiliary verbs mentioned above can also be employed as full verbs.
  - Function: They add meaning to the sentence and are essential for understanding the statement.

Comparison of English auxiliary and full verb

The fact that there are basically two different types of verbs often creates difficulties when learning English. To overcome this problem, you can remember one fundamental distinguishing feature: A main verb can appear alone – which means as the only verb – in the sentence. An auxiliary verb can only do this in certain cases, such as in short answers. Have a look at the following comparison with detailed characteristics:

Particularity	Auxiliary verb	Main/full verb
Occurrence:	Only appears in certain clauses or types of sentences, as for example in: questions negations clauses with perfect aspect ing-forms	Must be present in every sentence.
Number:	More than one can occur in a single sentence.	There can only be one in a sentence.
Characteristic in the sentence:	Always requires a main verb in the sentence and cannot appear as the only verb.	Does not require an additional verb and can occur as the only verb.
Negation:	Is usually accomplished by using ‘not’, examples: be: isn’t, was not, weren’t do: did not, doesn’t, don’t have: haven’t, has not	Typically, it is not directly negated, only by the aid of an auxiliary verb.

Special considerations in certain tenses

When learning English, problems regarding auxiliary and main verb mainly occur when using the tenses as certain ones have peculiar requirements. A particularity is that the auxiliary verb (if present) – and not the main verb – has to agree with the subject in number, person, etc. (compare concord for more details).

This can be tricky in cases when the full verb is also an auxiliary verb (which means the same verb is used twice). Examples:

“When does Mike do his homework?”
- Here, the first ‘do’ is the auxiliary verb (does), has to agree with the subject ‘Mike’ and be modified accordingly. It serves for constructing a question.
- Incorrect: “When do Mike does his homework?”
“She hasn’t had dinner yet.”
- Likewise in this sentence, the first ‘have’ as auxiliary verb must be conjugated according to the subject ‘she’ (and becomes ‘hasn’t’). It is required for the formation of the perfect. The second ‘have’ (had) is the main verb and past participle.
- Incorrect: “She haven’t had dinner yet.”

Auxiliary and full verbs in different tenses

Auxiliary and full verbs mainly occur together (belonging to one single predicate) in the compound tenses. Then, several auxiliary verbs (which means more than one) may be employed – but never more than one main verb. Compare some examples:

Tense	Example sentence	Auxiliary verb(s)	Full/main verb
Present simple	“Hanna is at home.”	none	is (base form: to be)
Present simple (negation)	“He doesn’t live here.”	does (base form: to do)	live (to live)
Present continuous	“Harold is waiting at work.”	is (to be)	waiting (to wait)
Present perfect simple	“They have left.”	have (to have)	left (to leave)
Present perfect simple passive	“A question has been asked.”	has (to have), been (to be)	asked (to ask)
Past simple	“We saw Mary.”	none	saw (to see)
Past simple passive	“Dinner was made.”	was (to be)	made (to make)
Future continuous	“We will be working.”	modal verb: will, be (to be)	working (to work)

Further explanations related to the ‘Difference between auxiliary and main verb’

The following explanations relate to the topic ‘Difference between English main/full verbs and auxiliary verbs’ and may also be helpful:

The English verb tenses
Conjugation of English verbs
Exercise 1: distinction between auxiliary and full verb

Difference: auxiliary and main verb