Since all natural habits are acquired by the past activities, and dispose for the future activities, of a being not absolutely perfect, but partly potential and partly actual, and subject to change, it follows that only finite beings can have habits. But, furthermore, beings that are not free, that have not control or dominion of their own actions, that have not freedom of choice, are determined by their nature, by a necessary law of their activity, to elicit the actions which they do actually elicit: such beings are by their nature _determinata ad unumn_; they are confined necessarily to the particular lines of action whereby they fulfil their rôle in the actual order of things. As Aristotle remarks, you may throw the same stone repeatedly in the same direction and with the same velocity: it will never acquire a _habit_ of moving in that direction with that velocity.(332) The same is true of plants and animals; for a habit in the strict sense implies not merely a certain mutability in its subject; it implies, and consists in, a stable modification of some power or faculty _which can have its activities directed indifferently in one or other of a variety of channels or lines_: the power or faculty which is the proper subject of a habit must be a _potentia dirigibilis vel determinabilis ad diversa_. Hence merely material powers of action—such as the mechanical, physical and chemical forces of inorganic nature, or the organic powers of living bodies, whether vegetative or merely sentient,—since they are all _of themselves_, of _their nature_, determined to certain lines of action, and to these only,—such powers cannot become the subjects of habits, of stable dispositions towards one line of action rather than another. “The powers of material nature,” says St. Thomas, “do not elicit their operations by means of habits, for they are of themselves [already adequately] determined to their particular lines of action.”(333) Only the spiritual faculties of free agents are, then, the proper seat of real habits. Only of free agents can we say strictly that “habit is second nature”. Only these can direct the operations of their intellect and will, and through these latter the operations of their sense faculties, both cognitive and appetitive, in a way conducive to their last end or in a way that deviates therefrom, by attaching their intellects to truth or to error, their wills to virtue or to vice, and thus forming in these faculties stable dispositions or _habits_.(334)