_Act_ and _potency_, in material things, are called _form_ and _matter_ respectively; hence, material substance is said to consist essentially of matter and form. The forms of natural things are usually divided into _substantial_ and _accidental_. The substantial form is commonly defined as that which gives the first existence to its matter--_quæ dat materiæ primum esse_, or _simpliciter esse_. It is sometimes defined, also, as that which gives the first existence to a thing--_quæ dat primum esse rei_. But this second definition is open to misconstruction; because, when the thing in question is a physical compound having a number of material parts, the form that gives to it--that is, to the compound essence--its first existence is its physical composition, which is not a substantial, but an essential, form, as we shall see presently. The accidental form is defined as that which gives an accidental mode of being--_quæ dat esse secundum quid_. This definition is universally admitted; but it is a remarkable fact that the examples of accidental forms given by most philosophers do not support it. Thus, the form of a statue and the form of a column are not forms giving to the marble any accidental mode of being, but are _the very modes of being_, which have resulted in the marble from the reception of suitable accidental acts. Therefore, what is called _the form_ of a statue is not a form _giving a mode of being_, but the mode itself, on account of which _we give_ to the marble _the name_ of a statue. Suarez and others have indeed pointed out the necessity of distinguishing the forms _dantes esse_ from the forms _dantes denominationem_; yet, even to this day, in our philosophical treatises, the definition of the former is almost exclusively illustrated by examples of the latter. True forms are _acts_, whilst modes of being are _actualities_; and therefore modes of being should not be called forms, but formalities. As, however, the word _form_ is in general use in this last sense also, the best thing we can do is to retain the term, and add to it a suitable epithet. I would call them _resultant forms_, or _consequential forms_; and in the same manner, when actuality is styled _act_, I would call it _consequential act_, or _complementary act_, that it may not be confounded with _act_ proper.