Your so right, our choices create our futures. What we think and feel also brings into our lives the reality. Your words are well spoken (written).

Have a Great day

Ron :)
www.thoughtelements.com

This may be a difference in dialects, but "in large part" is perfectly correct in US English, and "in a large part" would sound odd.

It modifies the verb "depends." It describes the extent to which the answer is dependent on whether or not we can think clearly. It does not describe the answer itself at all.

Yes, you are correct: it modifies the verb. The phrase "in large part" is almost always adverbial, answering the classic adverb question "to what extent?". It wouldn't make sense modifying a noun (like "answer"). It can modify an adjective, but in this case it modifies the verb, "depends". To what extent does it depend? In large part -- i.e., to a large extent.

(Adjectives, which modify nouns, answer questions like "which one?", "what kind?", "how many?", or "whose?"; adverbs, which modify verbs or adjectives or other adverbs, answer questions like "how?", "when?", "why?", or "to what extent?")

At the risk of sounding like I'm making an irrelevant remark, I'd say I most often see the expression inserted between two linguistic elements that are idiomatically connected to each other. "Depend in large part on something," "due in large part to something," and "thanks in large part to something." And cause-and-effect relations might have some bearing on these. Maybe, just maybe.