A Matter Of Perception

George Berkeley is important in philosophy through his denial of the existence of matter…He maintained that material objects only exist through being perceived.

 — Bertrand Russell 'The History Of Western Philosophy'

Putting The Negation In Negotiation

[For Spinoza] finite things are defined by their boundaries, physical or logical, that is to say, by what they are not: ‘all determination is negation’.

 — Bertrand Russell 'The History Of Western Philosophy'

Know Your Own Mind

There is thus, in all philosophy derived from Descartes, a tendency to subjectivism, and to regarding matter as something only knowable, if at all, by inference from what is known of mind.
 — Bertrand Russell 'The History Of Western Philosophy'

Without

Hobbes, as might be expected, is an out-and-out nominalist. There is, he says, nothing universal but names, and without words we could not conceive any general ideas. Without language, there would be no truth or falsehood, for ‘true’ and ‘false’ are attributes of speech.
 — Bertrand Russell 'The History Of Western Philosophy'