Quaeritur: Dr. Romero, are “second substance” and “first intention” in logic the same thing?
Respondeo: They are not exactly identical; secondary substances are either first intentions or second intentions. Primary substances are real, extramental substances, whereas secondary substances are beings of reason (entia rationis), that is, the ideas or intentions that we form in the mind. For example, that horse over there eating grass on the field is a primary substance, whereas the idea of 'horseness' that I form in my mind is a secondary substance. Now, these intentions or ideas come in two kinds: first intentions, which are ideas that directly represent reality, such as my idea of 'horseness', and second intentions, which are ideas about ideas, or ideas concerning the relationships between ideas, such as my idea of 'genus' and 'species'. Logic is the science of second intentions.