Question I: On the Essential Element or Object

St. Thomas, I-II, q. 18, a. 2.

101. Etymologically, an object is that which is set before someone; hence the object of a human act is everything that is set before the deliberation of reason and the choice of the will, and thus it also includes circumstances. In the present matter, however, it is taken in a stricter sense and designates that which, whether the thing is a thing or a person, is first and per se attained by the act, and thus it is distinguished from circumstances, which are not attained except secondarily and per accidens and by reason of another: to take another's property is the object of theft; little or much is a circumstance.

Concerning the essential objective element nothing general can be said, because, since all objects are singular, it varies with the different objects.