This is the whole list of those verbs which do not need a preposition to introduce another verb in infinitive:
- aimer/aimer mieux, aller, compter, croire, daigner, devoir, entendre, espérer, faire, falloir, (s')imaginer, laisser, oser, penser, pouvoir, prétendre, savoir, sembler, sentir, valoir mieux, venir, voir and vouloir.
In French when a verb is followed by a infinitive, four things can happen:
• the preposition de is placed between the verbs
• the preposition à is placed between the verbs
• another preposition that isn't de or à is placed between the verbs, for example pour
• there is no prepositions at all between the verbs.
There are some guidelines for helping to determine which preposition to choose but for the most part you need to memorise which prepositions go with each verb
apprendre à faire quelque chose - to learn how to do something
savoir + infinitive - to know how to do something
well, I kind of understand what you are saying, but is there some rule or guideline in place, to know what is needed where? Or just a moment, looking again at your answer. are you saying savoir never needs a preposition, whereas apprendre will always take à as a preposition?
There are some guidelines for helping to determine which preposition to choose but for the most part you need to memorise which prepositions go with each verb in the constructs:
conjugated verb + preposition + infinitive
conjugated verb + infinitive
the following modal verbs do not require a preposition before an infinitive that follows: devoir, pouvoir, savoir & vouloir
vous devez être fatigué you must be tired
savez-vous nager can you swim
je veux le faire I want to do it
the following verbs of the senses do not require a preposition before an infinitive that follows, namely: écouter, entendre, regarder, sentir & voir
je le vois venir - I see him coming