Now from like effects we presume like causes.

Many of the impressions of colour, sound, &c.

are confest to be nothing but internal existences, and to arise from causes, which no ways resemble them.

These impressions are in appearance nothing different from the other impressions of colour, sound, &c.

We conclude, therefore, that they are, all of them, derived from a like origin.
This principle being once admitted, all the other doctrines of that philosophy seem to follow by an easy consequence.