Benedict de Spinoza, THE ETHICS
Page: 18

nature of its own.

<<<<we have of external bodies, indicate rather the constitution of
our own body than the nature of external bodies. I have amply
illustrated this in the Appendix to Part I.

XVII. If the human body is affected in a manner which involves
the nature of any external body, the human mind will regard the
said external body as actually existing, or as present to
itself, until the human body be affected in such a way, as to
exclude the existence or the presence of the said external body.

>>>>>Proof--This proposition is self-evident, for so long as the
human body continues to be thus affected, so long will the human
mind (II. xii.) regard this modification of the body --that is
(by the last Prop.), it will have the idea of the mode as
actually existing, and this idea involves the nature of the
external body; therefore the mind (by II. xvi., Cor. i.) will
regard the external body as actually existing, until it is
affected, &c. Q.E.D.

<<<<bodies, by which the human body has once been affected, even
though they be no longer in existence or present.

>>>>>Proof--When external bodies determine the fluid parts of the
human body, so that they often impinge on the softer parts, they
change the surface of the last named (Post. v); hence (Ax. ii.,
after the Cor. of Lemma iii.) they are refracted therefrom in a
different manner from that which they followed before such
change; and, further, when afterwards they impinge on the new
surfaces by their own spontaneous movement, they will be
refracted in the same manner, as though they had been impelled
towards those surfaces by external bodies; consequently, they
will, while they continue to be thus refracted, affect the human
body in the same manner, whereof the mind (II. xii.) will again
take cognizance --that is (II. xvii.), the mind will again
regard the external body as present, and will do so, as often as
the fluid parts of the human body impinge on the aforesaid
surfaces by their own spontaneous motion. Wherefore, although