Please indicate the verb in this sentence'' I can swim in the river'' Here swim is an infinitive,so where is the main verb. Because infinitive can't be used as a verb.
Obviously you have been told many semi-truths. Like the idea that there can be only one verb in sentence. There does have to be a verb somewhere, but there is often more than one verb in a verb phrase.
As for infinitives, don't confuse the form of the verb (the infinitive, or present, or basic, form of the verb -- in this case, swim) from the construction the verb form is in. This particular infinitive form of swim is obligatory because it is the verb following can, a modal auxiliary verb, and all modal auxiliary verbs must be followed by the infinitive form of the next verb in the verb phrase.
Since it is the last verb in the verb chain that is the matrix verb (what you might call the "main verb"), and since the form is determined by the preceding auxiliary verbs, if any, the main verb can have any of the following forms:
- present tense form: He sings the song.
- past tense form: He sang the song.
- perfect participle form: He has sung the song.
- present participle form: He is singing the song.
(or, if the infinitive form is different from the present tense form, as it is with be
- infinitive He could be the singer.)
All of these may be the matrix verb. There may be up to four auxiliary verbs coming before the matrix verb, in what is called the Verb Chain, but it's the matrix verb that determines the meaning and grammar of the rest of the clause. As I used to tell my students, verbs have more fun.
The word swim here is a bare infinitive. This page from the website of University College London reads:
Infinitives with to are referred to specifically as TO-INFINITIVES, in order to distinguish them from BARE INFINITIVES, in which to is absent.
To-infinitive: Help me to open the gate
Bare infinitive: Help me open the gate
You can read on the Kaplan International website (as well as many other grammar websites and books), that the bare infinitive is used as the main verb (or matrix verb, according to John Lawler's answer) after auxiliary verbs such as 'do', 'should', 'can', and 'will'.
So now it should be obvious what the roles are:
can is an auxiliary verb that qualifies the main verb which is swim. Together, they form a simple verb phrase that is used to attribute to the subject of the sentence (in this sentence I) the ability (~can) to do the main action (here the main action is to swim).