I i didn't understand this very well ( non-finite verb)
  1. to infinitive or present infinitive
  2. perfect infinitiv
  3. bare infinitive
could you please explain this grammar ..
The word "finite" has to do with time. Of course "tense" also has to do with time.

Nearly all sentences have at least one main verb (or principle verb) which has a tense. This gives us the time period in which the "action" takes place. I'm sure you understand this.

But verbs have many forms, and some of them do not describe time periods. We say these forms are "non-finite."

The INfinitive is one of these.

Mary likes to swim.

Mary liked to swim.

"Likes" and "liked" are finite verbs. Each one has a tense, and describes a different time period.

"To swim" is the NON-FINITE infinitive, and is the same in both sentences. "To swim" doesn't tell us anything about the time period.

Gerunds and participles are also non-finite, and by themselves cannot describe a time period.

(Of course participles are ALSO used in the formation of certain tenses.)

I suppose the term "present infinitive" seems like an oxymoron. I think it just describes the most common form of the infinitive (to swim).

The "bare infinitive" appears to be the same as the "base form" of the verb.

It's simply the infinitive without the "to."

When "to" is included in the infinitive, some people still consider it a preposition, and some don't. (It's also called "a particle" (a very small grammatical element).

Some people call it "the infinitive marker."

When the infinitive is used together with a finite verb, we sometimes OMIT the "to."

When we do this, we sometimes say that this particular finite verb "takes the bare infinitive."

The rules about this are a little sketchy. You just have to learn which verbs use the "to" on a case-by-case basis.

She told me to go away.

She made me do it over again. (bare infinitive - no "to")

The "perfect infinitive" is a little weird.

He seems to take a long time to finish his homework.

(I guess you'd call this a present infinitive. - habitual behavior)

He seems to have taken a long time to finish his homework. (perfect infinitve - the action is complete.)
bare infinitive full infinitive perfect infinitive

= 'to' infinitive = to have + pp.

take to take to have taken

see to see to have seen

grow to grow to have grown

find to find to have found

like to like to have liked

walk to walk to have walked

have to have to have had

be to be to have been

decide to decide to have decided

do to do to have done

Continue the same patterns for all verbs.

CJ
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English does not have an infinitive form of the verb in the same way that French or Latin does. “To succeed”, for example, is not an infinitive verb; it's two words, the subordinator "to" and the verb "succeed'. Verbs requiring "to" are not 'to-infinitive verbs'; they are the plain form of the verb used with the separate subordinator "to" that appear in to-infinitival constructions like "I want to go shopping". Similarly, verbs used without "to", which are often called 'bare infinitives', are not infinitives at all. They are simply the plain form of the verb (without the subordinator "to") used in bare infinitival constructions. Note the difference between the terms 'infinitive' and 'infinitival construction'.

And there's no such thing as a 'perfect infinitive'. In "He seems to have lost it", for example, "have lost" is in the perfect tense, but this is another to-infinitival construction where "have" is the plain form of the verb, (not an infinitive). The expression "to have lost it" is a non-finite subordinate clause introduced by the subordinator 'to'; it's the complement of the verb "seems".

BillJ