We never note them by contrast with their absences.

The purpose of a discussion of such factors may be described as being to make obvious things look odd.

We cannot envisage them unless we manage to invest them with some of the freshness which is due to strangeness.
It is because of this habit of letting constant factors slip from consciousness that we constantly fall into the error of thinking of the sense-awareness of a particular factor in nature as being a two-termed relation between the mind and the factor.

For example, I perceive a green leaf.

Language in this statement suppresses all reference to any factors other than the percipient mind and the green leaf and the relation of sense-awareness.