derived from this source. It will then be incumbent on us, if we would
maintain our doctrine, to produce the impression, or lively perception,
which corresponds to it.

15. Secondly. If it happen, from a defect of the organ, that a man is
not susceptible of any species of sensation, we always find that he is
as little susceptible of the correspondent ideas. A blind man can form
no notion of colours; a deaf man of sounds. Restore either of them that
sense in which he is deficient; by opening this new inlet for his
sensations, you also open an inlet for the ideas; and he finds no
difficulty in conceiving these objects. The case is the same, if the
object, proper for exciting any sensation, has never been applied to the
organ. A Laplander or Negro has no notion of the relish of wine. And
though there are few or no instances of a like deficiency in the mind,
where a person has never felt or is wholly incapable of a sentiment or
passion that belongs to his species; yet we find the same observation to
take place in a less degree. A man of mild manners can form no idea of
inveterate revenge or cruelty; nor can a selfish heart easily conceive
the heights of friendship and generosity. It is readily allowed, that
other beings may possess many senses of which we can have no conception;
because the ideas of them have never been introduced to us in the only
manner by which an idea can have access to the mind, to wit, by the
actual feeling and sensation.

16. There is, however, one contradictory phenomenon, which may prove
that it is not absolutely impossible for ideas to arise, independent of
their correspondent impressions. I believe it will readily be allowed,
that the several distinct ideas of colour, which enter by the eye, or
those of sound, which are conveyed by the ear, are really different from
each other; though, at the same time, resembling. Now if this be true of