PHYSICAL anp LITERARY. 13 
exiftence of immaterial fubftances, becaufe 
thefe do not exhibit themfelves to our fenfes. 
Power is a property or quality, of which 
none of our external fenfes afford us the per- 
ception; and therefore our want of percepti- 
on of power, does not more conclude a nega- 
tion of power to matter, than to fpirit. In 
general, we have no means to come at the 
_ knowledge of .a caufe, but by the effec? pro- 
duced. We cannot, @ priori, conclude, 
that animate beings are endued with any fort 
of powers, more than inanimate. Experience 
is here our only guide. We find by experi- 
-ence man to bea reafoning being, endued 
with many powers and faculties: and, by the 
fame experience, we find matter to be endu- 
ed with certain powers and faculties. Both 
are difcovered by the effects produced; and 
we have no other means to make a difcovery. 
We feea ftone fall without any external im- 
pulfe. From that effect we have a juft foun-. 
dation to conclude, that the ftone has a pow- 
er of moving itfelf. And, if we have not a 
juft foundation to make this conclufion, we 
have not a juft foundation to make this other 
_conclufion, that a man has a power of felf- 
motion when we fee him walking. And af- 
ter 
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