Q: Dear Sage
A warlock’s invocations include “relatively simple” somatic components. Can you use them while grappling? What about while your hands are full or bound?
--Jeff and Don
A: No and no.
Even though the somatic components are simple enough to allow a warlock to ignore arcane spell failure while wearing light armor, they’re still considered somatic components.
Thus, you can’t use an invocation while in a grapple or while pinned (because you can’t cast spells with somatic components in those situations; PHB p170).
Since you must have one hand free to cast a spell with a somatic component (PHB p174), you can’t use an invocation if your hands are full, tied, or otherwise occupied.
About the Author
The Sage is a mammal classified in the bear family, Ursidae, native to central and southern China. Debate continues as to whether he is truly a bear or more related to the raccoon rather than the bear, or perhaps in a family of his own. When not eating bamboo and answering rules questions, he works under the nom de plume of Andy Collins as an RPG developer in Wizards of the Coast R&D, where his development credits include Complete Mage, Dragon Magic, and the Player's Handbook v.3.5. He can be easily recognized by his large, distinctive black patches around the eyes, ears and on his rotund body.