When do we add a "de" in between 2 verbs?

[Joseph]

For example, "i want to eat apples"
So, is it, "Je veux manger des pommes" or "Je veux de manger des pommes"?
When do we know when to add the "de"
Any other instances where "de" is used?

[Neil Coffey]

As you'll appreciate, it's difficult to give rules that work in all cases, because to some extent, speakers use a particular construction "just because" that's what they've got used to using. However, here are some guidelines. Note that the choice depends on the first verb of the pair:

No preposition between the verbs:
- so-called "modal" verbs (vouloir, devoir, pouvoir, savoir)
- verbs of stating (dire but also near synonyms like avouer, affirmer, croire/penser/considérer, prétendre...)
- verbs giving an opinion about the action of the second verb (préférer, aimer, détester, souhaiter)
- usually, verbs of motion (aller, monter...)
- a few special "causal" verbs that indicate the object of the first verb being forced to carry out the action of the second verb (laisser, faire, also envoyer)-- note that other verbs indicating "starting" of an action generally take à, and verbs of "commanding" take de

Preposition à used:
- most cases when there is a notion of starting the action of the second verb (apprendre à..., commencer à..., se mettre à..., conduire/mener/pousser/inciter qn à..., décider qn à..., se décider à..., viser à...)
- some cases where à would have been used with a noun anyway (with overlap with the previous subcategory), e.g. on l'a poussé au crime/à commettre des délits

Preposition de used
- many verbs of "commanding" or recommending, including commanding oneself: commander/demander/persuader/recommander/conseiller (à) qn de faire qch
- when there is a notion of "stopping" the action: arrêter, cesser, empêcher
- many cases where de would have been used with a noun, and where de carries a genuine value of "from", "of", "for": accuser/remercier/soupçonner qn d'avoir fait qch

[Joseph]

Thanks so much Neil.