The Classification of Words

§ 185. The prop-word one (or substituting one) is a pro­noun used anaphorically, i. e. to replace some antecedent, a noun (or a noun combination) previously mentioned as in The work is a remarkable one. (Galsworthy) One, naturally, assumes the meaning of its antecedent.
It replaces, as a rule, countable nouns, both those de­noting living beings and those naming inanimate things.
She is a woman too, she looks a rather nice one (Randall). And she has a nice figure, a really nice one. (Randall) It has a number opposite ones: Let me have some pens — I'd like new ones.
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The prop-word one may be preceded by the definite and the indefinite articles, the demonstrative pronouns, adjec­tives, nouns, numerals, participles, etc., like nouns, not pro­nouns.
My new dress, the nylon one, is a dream. (Daily Worker). This story, and it is a good and exciting one, will be a roaring success. (Daily Worker).
The function of one is often purely structural, to support the preceding adjectfve or to show that the preceding word is used attributively. Cf. the silk and the silk one.
Look at those bindings, absolutely tattered. It is time we had new ones.
§ 186. Summing up, we may say that the pronouns ere not united by any morphological categories, or syntactical functions. So they cannot be regarded as a part of speech.
On the other hand they constitute a separate class of words with peculiar meanings and references to the world of reality.
All of them are of double nature, as they combine their peculiar meanings with certain properties of definite parts of speech (nouns, adjectives, numerals, adverbs).
The drawing below gives an idea of this

nouns	СЛ С .. 3 о . a о t_ a.
adjectives
numerals
adverbs