ffftorc known to us \ than that of Spirits upon Bodies , or of Bodies npon^ 
Spirits; and yet moft men admire nothing but , believing to know 
the ethir : whereas he Judges , that all things being well examined, 
the A^ionof Bodies upon Bodies is no more conceivable, than that of 
Spirits upon Bodies. Mean while the opinion of the Authour touch- 
ingthis fubjed, is, That the union of Soul and Body confifts onely in 
this, that certain motions of the Body are followed by certain Coj^i^ 
miens oi the Soul , and , on the contrary , that certain Thoughts 
of the Soul ars followed by certain M&tiens of the Body. And , ha- 
ving fuppofed, that Bodies are faid to aft upon one another , when they 
(caufefome change fuitable to Extenfion and Spirits to ad upon one 
another, when ihey caufe fome change fuitable to a Thought • he in- 
fers, that when a Body ads .upon a Spirit , that cdnnot be by caufing: 
any change of motion, of figure^ or pares, as having none of all thcfe^ 
nor when a Spirit ads upon a Body , that cannot be by produ« 
cing any change of Thought, as having none : But , when this Body, or 
its motion, or figure, or other thing, depending upon its nature £:m 
he perceived by a Spirit^ fo as, upon that occafion , this Spirit has 
thoughts, it had not before, it may be faid, that the Body has aded upon 
this Spirit,for as much as it has caufed all the change in it, whereof it was 
capable according to its nature. 
In the Sixtk ^ After He hath fHew'd , what is to be undcrftood by 
what we call Sml, and by what we call Bodj , -he labours to make it outj 
thrit we ire much more affurcd of the Exiflencc of the Soul , than of' 
that of the Body, which he conceives he can prove from hence, that 
we cannot doubt, that we think , bceaufe even doubting is thinking y„ 
But one may doubt, whether one hasa body, for fever*! reafons , 
which he allcdgcs, and thinks fo cogent , that he concludes, it is not 
evident to Mm by the light of reafon , that he has a Body* But fuppo- 
fing, there be Bodies, he examines^ what are the Operations, that belong: 
to the Soul, and what thofe, that belong to the Body • and laftlyj 
what thofe, thatrefult from the Union of both: And. tlien explains^ 
how all thofe operations are performed , and particularly, Senfation • 
where hcfhcws, that the Nerves, holding atone end to the Brain^ 
whereof they are but Allongations , and being at the other end ex- 
tended to the extremities of the Body ^ w.hen an Objcd comes to 
touch thofe exterior ends of the Nerves , the interior ones in the 
Brain are prefently (haken , and eaufe different fenfations according 
to the diverfitie of Nerves , and the differing manner , in which 
they are (haken» And to (hew^ tliat *tis this fhakirg, that caufes Senfa-! 
ti©n 5 he notes, that if any thing fliakcs the interior parts of the Nerves^ 
though the obj>d be abfenc , the Soul has prefently the fame fen- 
fations-' 
