99. So likewise when we attempt to abstract extension and motion from all
other qualities, and consider them by themselves, we presently lose sight
of them, and run into great extravagances. All which depend on a twofold
abstraction; first, it is supposed that extension, for example, may be
abstracted from all other sensible qualities; and secondly, that the
entity of extension may be abstracted from its being perceived. But,
whoever shall reflect, and take care to understand what he says, will, if
I mistake not, acknowledge that all sensible qualities are alike
sensations and alike real; that where the extension is, there is the
colour, too, i.e., in his mind, and that their archetypes can exist only
in some other mind; and that the objects of sense are nothing but those
sensations combined, blended, or (if one may so speak) concreted
together; none of all which can be supposed to exist unperceived.

100. What it is for a man to be happy, or an object good, every one may
think he knows. But to frame an abstract idea of happiness, prescinded
from all particular pleasure, or of goodness from everything that is
good, this is what few can pretend to. So likewise a man may be just and
virtuous without having precise ideas of justice and virtue. The opinion
that those and the like words stand for general notions, abstracted from
all particular persons and actions, seems to have rendered morality very
difficult, and the study thereof of small use to mankind. And in effect
the doctrine of abstraction has not a little contributed towards spoiling
the most useful parts of knowledge.

101. OF NATURAL PHILOSOPHY AND MATHEMATICS.--The two great provinces
of speculative science conversant about ideas received from sense,
are Natural Philosophy and Mathematics; with regard to each of these
I shall make some observations. And first I shall say somewhat of
Natural Philosophy. On this subject it is that the sceptics triumph.