The highest power of the soul and the exclusive possession of man (the faculties mentioned before are found also in animals) is the rational soul. This is at first simply a potentiality. Actually it is a _tabula rasa_, an empty slate, a blank paper. But it has the power (or is the power) of acquiring general ideas. Hence it is called hylic or material intellect, because it is like matter which in itself is nothing actual but is potentially everything, being capable of receiving any form and becoming any real object. As matter receives sensible forms, so the material intellect acquires intelligible forms, _i. e._, thoughts, ideas, concepts. When it has these ideas it is an _actual intellect_. It is then identical with the ideas it has, _i. e._, thinker and thought are the same, and hence the statement that the actual intellect is "intelligent" and "intelligible" at the same time. As matter is the principle of generation and destruction the rational soul, which is thus shown to be an immaterial substance, is indestructible, hence immortal. And it is the ideas it acquires which make it so. When the rational soul is concerned with pure knowledge it is called the _speculative_ or _theoretical intellect_. When it is engaged in controlling the animal powers, its function is conduct, and is called the _practical intellect_. The rational soul, _i. e._, the speculative intellect, is separable from the body and needs it not, though it uses it at first to acquire some of its knowledge. This is proved by the fact that whereas the corporeal powers, like the senses, are weakened by strong stimuli, the reason is strengthened by hard subjects of thought. Old age weakens the body, but strengthens the mind. The activities of the body are finite; of the mind, infinite.