a. The _Axioms_: That no substance has that of it self, which it can loose, without ceasing to be, what it is: That every body may loose of its motion, till it have no more left, without ceasing to be a Body: That we cannot conceive but two sorts of substances, _vid._ a _Spirit_ (or _That which thinketh_) and a _Body_, wherefore they must be considered as the Causes of all, that happens, and what cannot proceed from the one, must necessarily be adscribed to the other: That to _Move_, or to cause motion, is an Action: That an Action cannot be continued but by the Agent, who began it. b. The _Conclusions_: That no _Body_ hath Motion of it self: That the First Mover of Bodies not a Body: That it cannot be but a _Spirit_, that is the First Mover: That it cannot be but the same Spirit, who has begun to move Bodies, that continues to move. In the _Fifth_, He treats of the Union of the Body and Soul, and the manner, how they act one upon the other; and esteems it not more difficult to conceive the Action of Spirits upon Bodies, and of Bodies upon Spirits, than to conceive the Action of Bodies upon Bodies: the cause of the great difficulty in understanding the two former, arising (according to him) from thence, that we will conceive the one by the other, not considering, that every thing acting according to its own nature, we shall never know the action of one Agent, if we will examine it by the notions we have of another, that is of a quite differing nature. Here he notes, that the Action of Bodies upon Bodies is not {309} more known to us; than that of Spirits upon Bodies, or of Bodies upon Spirits; and yet most men admire nothing but _this_, believing to know the _other_; whereas he Judges, that all things being well examin'd, the Action of Bodies upon Bodies is no more conceivable, than that of Spirits upon Bodies. Mean while the opinion of the Authour touching this subject, is, That the union of Soul and Body consists onely in this, that certain motions of the Body are followed by certain _Cogitations_ of the Soul, and, on the contrary, that certain Thoughts of the Soul are follow'd by certain _Motions_ of the Body. And, having supposed, that Bodies are said to act upon one another, when they cause some change suitable to Extension; and Spirits to act upon one another, when they cause some change suitable to a Thought; he infers, that when a Body acts upon a Spirit, that cannot be by causing any change of motion, of figure, or parts, as having none of all these; nor when a Spirit acts upon a Body, that cannot be by producing any change of Thought, as having none: But, when this Body, or its motion, or figure, or other thing, depending upon its nature, can be perceived by a Spirit, so as, upon that occasion, this Spirit has thoughts, it had not before, it may be said, that the Body has acted upon this Spirit, for as much as it has caused all the change in it, whereof it was capable according to its nature.