By this means we accompany our ideas with a kind of reflection, of which custom renders us, in a great measure, insensible.

A person, who desires us to consider the figure of a globe of white marble without thinking on its colour, desires an impossibility but his meaning is, that we should consider the figure and colour together, but still keep in our eye the resemblance to the globe of black marble, or that to any other globe of whatever colour or substance..