When we have an idea we embrace unconsciously but really the whole extent of reality. In other words, ideas have a peculiar quality: they are predictable of many (universal). The first contact with a new object yields a universal idea. It will be an imperfect one, but it is a universal idea nevertheless. For example, “something black”. This is a universal idea. Then I realise that it is a deer. Concepts like, being, beautiful, man, woman, child, dog, house, stone, etc., are applicable to many realities. Hence all ideas are universal.
Ideas are universal yet reality known is individual
Every reality which actually exists is individual. By the principle of no-contradiction no reality can be at the same time and under the same aspect one and multiple. In other words, in our everyday knowledge we know first the singular, individual, concrete people and objects (eg. concept of ‘human person’ as this man or this woman). But they are known by the whole person, intellect and senses combined. The intellect knows only the intelligible features of the object and they coincide with its substantial form which is the same in all individuals of the same species. Therefore, to know only the substantial form of an object is to know only that which the object has in common with other individuals of the same species (eg. ‘treeness’, ‘cowness’ etc.). What distinguishes one individual from another is relation to quantified matter. But a spiritual power such as the human intellect cannot directly know quantified matter. Therefore, it does not know that which distinguishes one individual from another. But in our ordinary knowledge we always use intellect and senses together. The intellect gives us the universal intelligible features, the senses apply and restrict them to particular individuals.
Judgement is the “second” operation of the intellect. To judge means to affirm or deny a thing. Every concept presupposes a judgement since it originates in a judgement. For example, “This is a cow”; “It is not a tree”. Both are judgements. Often what would seem to be a mere concept is actually a simple judgement. Thus judgement is the central point of our intellectual life. There is no consciousness of the object of our intellect until we have an intellectual expression of it. This expression takes the form of judgement and we have knowledge.
Inference is the third operation of the intellect
Inference (reasoning) is the “third’ operation of the intellect. In order to acquire new knowledge the intellect has recourse to inferred truths using deduction and induction. These methods are used for reaching evidences and proving that such and is or is not the case. Mathematics (which uses abstract logical forms) and experimental sciences (which use the method of hypothesis and verification through experimentation) also use ‘reason’ in order to acquire new knowledge, though the laws and theories founded on the experimental method cannot be definitely true and unchangeable. Nevertheless, whatever law or theory which is verified is considered as true due to the logical law that necessarily governs the procedure.