1a 2ae q13 a4: Whether choice is of those things only that are done by us? Yes.

Electio semper est humanorum actuum quia necesse est ut id quod est ad finem: vel sit actio, vel res aliqua (interveniente aliqua actione, per quam facit id quod est ad finem, vel utitur eo).

Choice is always in regard to human acts because the means must needs be: either an action, or a thing (with some action intervening whereby man either makes the thing which is the means, or uses it).