English Usage Guides (1974, vol. 7, 6)

Peter Gawn
(Terminology Update, Volume 7, Number 6, 1974, page 4)


Which relative pronoun, that or which ?


Should a relative clause always be introduced by which, or should that be used, and if so, when?


(a) The cat sat on the mat, which I had just washed, and went to sleep.

(b) The cat sat on the mat that I had just washed and went to sleep.


The authorities are divided. Those who advocate the distinction do so because in the example, (a) suggests that there was only one mat, and (b) that the muddy-footed cat sat on the newly-washed mat in preference to the other, unwashed, mats.

The second interpretation of the sentence makes the relative clause a defining one: out of the general "mat" category it identifies a particular mat. The clause in (a) is non-defining; it provides information about the mat that is not essential to the meaning of the main sentence. Without the relative clause in (a), the sentence makes sense; without the clause in (b), something is lost.

The use of that or which is therefore linked to the identification of the relative clause as defining (or restrictive or subordinate) or non-defining (or non-restrictive, coordinate or commenting). The non-defining clause is usually parenthetical, set off by commas, the implication being that the parenthesis can be omitted without affecting the message.

Most of the authorities recognize the distinction, but they note that which is tending to be used in all relative clauses, supplanting the older that (Jespersen 34.21). With two exceptions, those who express an opinion regret this trend and recommend reserving that for defining and which for non-defining clauses. Of course, it is not always easy to distinguish the clauses in this way, and the ear must then be used to decide the pronoun (Plain Words, p. 121). The two exceptions to what would otherwise be a consensus are Plain Words and Wood, both, incidentally British. Wood says that for defining clauses the writer is at liberty to use either word according to what seems the better in a particular context, and Plain Words that there is no justification for insisting on the distinction, and that that is becoming less common in good writing.

Is he right? Does the distinction matter? I think so. Sometimes it is essential, to avoid ambiguity; at all times, it shows that the writer is aware of his craft. "The discrimination between which and that is one of the marks of a stylist" (Partridge p. 364). "The careful writer, watchful for small conveniences, goes which-hunting, removes the defining whiches, and by so doing improves his work" (Strunk p. 59).

Three other points need to be mentioned:

  1. that may often be omitted (The cat sat on the mat I had just washed.);
  2. who is generally used for persons (The cat greeted the man who had just come in.);
  3. for euphony, which is used in a defining clause following demonstrative that (That is the mat which I had just washed.).


Although which is not grammatically incorrect as the relative pronoun in a defining clause, the consensus favours that. The careful writer observes the distinction. Relative clause: use that to introduce defining and which to introduce non-defining (commenting) relative clauses.


CGSM: Style Manual for Writers and Editors, Queen’s Printer, 1962.
Jespersen: Essentials of English Grammar, O. Jespersen, Geo. Allen & Unwin, 1987.
Partridge: Usage & Abusage, E. Partridge, Penguin, 1969.
Plain Words: The Complete Plain Words, E. Gowers, David R. Godine, Publishers, Inc., 1988.
Wood: Current English Usage, A Concise Dictionary, F.T. Wood, Macmillan, 1981.

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