In this form, the exposition is of the sort styled definition, in the narrowest sense of the word,---definitio per genus et differentiam:---exposition effected by indication given of the next superordinate class of objects in which the object in question is considered as comprehended, together with that of the qualities peculiar to it with reference to the other objects of that same class.

The import of the word faculty being still more extensive tban that of the word power, as may be seen by its assuming the adjunct passive, the word power is, in a certain sense, not unsusceptible of the definition per genus et differentiam: but to complete the exposition, an exposition by periphrasis may perhaps require to be added.