<p>i. An animal's actions are largely determined by instinct.
ii. Animals mainly have their instinct as a determinant for behavior.</p>
<p>Version (i) is better, and I can sort of "feel" that, but I still cannot quite put into words what makes (ii) awkward. Any input?</p>
<p>One is better than two because we simply don’t say determinant for…, but determinant of. Also, The more the sentence is precise the more it is better.</p>
<p>I have a know-how. Verb.>Adj.>Noun. Verb is the first choice. Not absolutely right, but it is really a shortcut for sentence improving.</p>