What the Intellect Knows in Material Things

In this fife in which man’s soul and body are substantially united, the object of the human intellect is theessences of material things. The intellect knows such essences in universal by acquiring ideas or concepts in the manner already described. By a second act which is a kind of reflex act or reflection, the intellect knows material things in individual. The intellect inquires, in this bodily world,“What kind of thing is that?” When it knows the kind or essence, it can advert to the individual things and say,“Yes, these are things of that kind.” Primarily and directly, the intellect knows universals; secondarily and reflexly,the intellect knows singulars, that is, individual material things.

The human intellect is a created and finite power. Therefore it cannot perfectly know the infinite. The intellect can know potential infinity, which means unlimited possibility. The intellect itself has potential infinity inasmuchas it is never filled up, but can always know something more. Butthe intellect cannot know perfectly actual infinity.

Contingent things (that is, changeable things; things that have not in themselves a necessity for existing) are the direct object of sense-knowledge. The intellect, by its secondary and reflex act, can know singulars; hence the intellect can know contingent things. The intellect also knows the necessary and universal principles that are back of contingent things, such, for instance, as the truth that movement always requires a mover.

The human intellect cannot know the future except in cause. To know a thing in cause is to foresee the effects which will come from existing and necessitating causes. Thus astronomersknow, even centuries before the event, the exact time at which an eclipse of the sun is to occur. To know the future, not merely in cause, but in itself, is beyond creatural power; such knowledge belongs to God alone. The human intellect has an abundance of conjectural knowledge of the future; such knowledge isa reasonable guess or supposition; it is usually founded upon experience of what has happened in the past.