The Stoics, however, would not agree with Plato and Aristotle so far as to allow to formal and final causes a place side by side with this acting force or efficient cause. If in general anything may be called a cause which serves to bring about a definite result [287]—and various kinds of causes may be distinguished, according as they bring about this result directly or indirectly, by themselves alone or by the help of others [288]—in the highest sense there can be, according to the Stoics, only one acting or efficient cause. The form is due to the workman, and is therefore only a part of the efficient cause. The type-form is only an instrument, which the workman employs in his work. The final cause or end-in-chief, in as far as it represents the workman’s intention, is only an occasional cause; in as far as it belongs to the work he is about, it is not a cause at all, but a result. There can be but one pure and unconditional cause, just as there can be but one matter; and to this efficient cause everything that exists and everything that takes place must be referred. [289] [(b) Character of this efficient cause.] In attempting to form a more accurate notion of this efficient cause, the first point which deserves attention is, that the Stoics believed every kind of action ultimately to proceed from one source. For how could the world be such a self-circumscribed unity, such an harmonious whole, unless it were governed by one and the same force? [290] Again, as everything which acts is material, the highest efficient cause must likewise be considered material; and since all qualities and forces are produced by vapour-like or fiery elements, can it be otherwise with the highest acting force? [291] Everywhere warmth is the cause of nourishment and growth, life and motion; all things have in themselves their own natural heat, and are preserved and kept in life by the heat of the sun. What applies to parts of the world must apply to the world as a whole; hence heat or fire is the power to which the life and the existence of the world must be referred. [292]