I saw him climb over the fence. (= I saw that he climbed…)
I have never heard this group perform this song. (= I have never heard this song performed by this group.)

After these verbA part of speech that expresses an action or a state. E.g.: John seldom plays tennis.s the infinitive expresses a completeA concept, related to the perfect aspect, expressing that an action has finished. E.g.: He’s finished university.d actionA general term expressing that somebody or something does something. If we mean an action in progressAn action is in progress when it is happening. E.g.: When I arrived he was surfing. ("he was surfing"), a present participle is used:

I saw him climbing over the fence. (= I saw him as he was climbing…)
I heard him singing in the bathroom. (= I heard him as he was singing…)

Note that only in passive voiceThe form of the transitive verb that shows whether the subject acts (active voice) or is acted upon (passive voice). is to inserted before the infinitive.

He was seen to climb over the fence.

If a participle was used in the active sentence, in passive voice a continuousThe aspect expressing duration, formed with be + verb-ing. E.g.: What are you doing? infinitive is used:

He was seen to be climbing over the fence.

BE + superlative adjective + TO + infinitive
The use of infinitives IT IS / WAS + adjective + (FOR SOMEBODY) TO + infinitive