We cannot observe external things without some degree of Thought; nor…

The solution is, that we do not see the image on the retina at all, we only see by means of it.

Facts are the materials of science, but all Facts involve Ideas. Since, in observing Facts, we cannot exclude Ideas, we must, for the purposes of science, take care that the Ideas are clear and rigorously applied.

We perceive by 'means' of a medium and 'by means' of impressions on the nerves: but we do not (by our senses,) perceive either the medium or the impressions on the nerves.

The Sight cannot decompose a compound colour into simple colours, or distinguish a compound from a simple colour

Coexistent polarities are fundamentally identical.

When a series of progressive numbers is given as the result of observation, it may generally be reduced to law by combinations of arithmetical and geometrical progressions. A true formula for a progressive series of numbers cannot commonly …