In his book, Russell distinguishes several types of knowledge. He first distinguishes knowledge of truths, and of things.

"the sense in which what we know is true (...) i.e. to what are called judgements (...) may be described as knowledge of truths."

"knowledge of things (...) (is knowing) sense-data"

So I think an example of knowledge of truths would be 'This chair is brown', wheres knowledge of things would be the act of seeing the chair.

But my confusion began when he further distinguished knowledge of things into two types: knowledge of things by acquaintance and by description. Description, he explains,

"The table is 'the physical object which causes such-and-such sense-data'. This describes the table by means of the sense-data."

But I don't see why description falls under knowledge of things. Since description is a set of predicate about sense-data, not a set of sense-data itself, shouldn't description be considered as knowledge of truths? Or am I misunderstanding his terminology completely?

  • Russell's distinction between knowledge-of and knowledge-that is often seen as obscure:"Certainly we do know things, persons, and places by acquaintance, but to do so is generally to know that something is true of them and is at least to know how to recognize them", see Knowledge and Belief. What he could have in mind is that description somehow evokes sense data (remembered or imagined), which then becomes the object of knowledge-of. He does say that it "involves" knowledge of truths.
    – Conifold
    Aug 14 '21 at 10:40
  • a description " the so and so" is not a sentence, hence not a proposition, hence not a truth Aug 14 '21 at 11:56
  • @FloridusFloridi A description is not, but knowledge by description can be. "To know some thing or object by a definite description is to know that it is the so-and-so or that the so-and-so exists, i.e., that there is exactly one object that is so-and-so (Russell 1912: 82–3)", SEP. Russell also says that knowledge by description "always involves… some knowledge of truths as its source and ground (1912: 72–3)".
    – Conifold
    Aug 14 '21 at 12:52
  • I wanted to insist on a basic point: a noun + a relative clause is not a sentence, but a nominal syntagm; ; I think it is that point that caused the confusion in the OP's mind. Aug 14 '21 at 13:08
  • 1
    It is the opposite with acquaintance:"We shall say that we have acquaintance with anything of which we are directly aware, without the intermediary of any process of inference or any knowledge of truths... though it would be rash to assume that human beings ever, in fact, have acquaintance with things without at the same time knowing some truth about them." He clearly attributes "experiential" aspect to "sense data", irreducible to propositions, but struggles with knowledge-of by description, which has to be mediated by them. Hence my guess that such aspect is added by memory or imagination.
    – Conifold
    Aug 14 '21 at 16:49

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