most profound philosophy; which might merit our attention, were it
requisite to dive so deep, in order to discover arguments and
reasonings, which can so little serve to any serious purpose. It is
universally allowed by modern enquirers, that all the sensible qualities
of objects, such as hard, soft, hot, cold, white, black, &c. are merely
secondary, and exist not in the objects themselves, but are perceptions
of the mind, without any external archetype or model, which they
represent. If this be allowed, with regard to secondary qualities, it
must also follow, with regard to the supposed primary qualities of
extension and solidity; nor can the latter be any more entitled to that
denomination than the former. The idea of extension is entirely acquired
from the senses of sight and feeling; and if all the qualities,
perceived by the senses, be in the mind, not in the object, the same
conclusion must reach the idea of extension, which is wholly dependent
on the sensible ideas or the ideas of secondary qualities. Nothing can
save us from this conclusion, but the asserting, that the ideas of those
primary qualities are attained by _Abstraction_, an opinion, which, if
we examine it accurately, we shall find to be unintelligible, and even
absurd. An extension, that is neither tangible nor visible, cannot
possibly be conceived: and a tangible or visible extension, which is
neither hard nor soft, black nor white, is equally beyond the reach of
human conception. Let any man try to conceive a triangle in general,
which is neither _Isosceles_ nor _Scalenum_, nor has any particular
length or proportion of sides; and he will soon perceive the absurdity
of all the scholastic notions with regard to abstraction and
general ideas.[31]

[31] This argument is drawn from Dr. Berkeley; and indeed most
of the writings of that very ingenious author form the best
lessons of scepticism, which are to be found either among