LV.
It is a Paradox that Experience should lead us to truths confessedly universal, and apparently necessary, such as the Laws of Motion are. The Solution of this paradox is, that these laws are interpretations of the Axioms of Causation. The axioms are universally and necessarily true, but the right interpretation of the terms which they involve, is learnt by experience. Our Idea of Cause supplies the Form, Experience, the Matter, of these Laws. (iii. 8.)
LVI.
Primary Qualities of Bodies are those which we can conceive as directly perceived; Secondary Qualities are those 16 which we conceive as perceived by means of a Medium. (iv. 1.)
LVII.
We necessarily perceive bodies as without us; the Idea of Externality is one of the conditions of perception. (iv. 1.)
LVIII.
We necessarily assume a Medium for the perceptions of Light, Colour, Sound, Heat, Odours, Tastes; and this Medium must convey impressions by means of its mechanical attributes. (iv. 1.)
LIX.
Secondary Qualities are not extended but intensive: their effects are not augmented by addition of parts, but by increased operation of the medium. Hence they are not measured directly, but by scales; not by units, but by degrees. (iv. 4.)