is an addition to a magnitude already
existing." Therefore in habits also there is no increase without
addition.

Obj. 2: Further, habit is not increased except by means of some
agent. But every agent does something in the passive subject: for
instance, that which heats, causes heat in that which is heated.
Therefore there is no increase without addition.

Obj. 3: Further, as that which is not white, is in potentiality to be
white: so that which is less white, is in potentiality to be more
white. But that which is not white, is not made white except by the
addition of whiteness. Therefore that which is less white, is not
made more white, except by an added whiteness.

_On the contrary,_ The Philosopher says (Phys. iv, text. 84): "That
which is hot is made hotter, without making, in the matter, something
hot, that was not hot, when the thing was less hot." Therefore, in
like manner, neither is any addition made in other forms when they
increase.

_I answer that,_ The solution of this question depends on what we
have said above (A. 1). For we said that increase and decrease in
forms which are capable of intensity and remissness, happen in one
way not on the part of the very form considered in itself, through
the diverse participation thereof by the subject. Wherefore such
increase of habits and other forms, is not caused by an addition of
form to form; but by the subject participating more or less
perfectly, one and the same form. And just as, by an agent which is
in act, something is made actually hot, beginning, as it were, to
participate a form, not as though the form itself were made, as is
proved in _Metaph._ vii, text. 32, so, by an intense action of the
agent, something is made more hot, as it were participating the form
more perfectly, not as though something were added to the form.

For if this increase in forms were understood to be by way of
addition, this could only be either in the form itself or in the
subject. If it be understood of the form itself, it has already been
stated (A. 1) that such an addition or subtraction would change the
species; even as the species of color is changed when a thing from
being pale becomes white. If, on the other hand, this addition be
understood as applying to the subject, this could only be either
because one part of the subject receives a form which it had not
previously (thus we may say cold increases in a man who, after being
cold in one part of his body, is cold