Chapter Thalamocœle to That of T by Webster's Dictionary (1913 Edition)

That was formerly sometimes used with the force of the article the, especially in the phrases that one, that other, which were subsequently corrupted into th'tone, th'tother

Upon a day out riden knightes two . . .
That one of them came home, that other not.

Chaucer.

3. As a relative pronoun, that is equivalent to who or which, serving to point out, and make definite, a person or thing spoken of, or alluded to, before, and may be either singular or plural.

He that reproveth a scorner getteth to himself shame.

Prov. ix. 7.

A judgment that is equal and impartial must incline to the greater probabilities.

Bp. Wilkins.

If the relative clause simply conveys an additional idea, and is not properly explanatory or restrictive, who or which (rarely that) is employed; as, the king that (or who) rules well is generally popular; Victoria, who (not that) rules well, enjoys the confidence of her subjects. Ambiguity may in some cases be avoided in the use of that (which is restrictive) instead of who or which, likely to be understood in a coördinating sense. Bain.

That was formerly used for that which, as what is now; but such use is now archaic.

We speak that we do know, and testify that we have seen.

John iii. 11.

That I have done it is thyself to wite [blame].

Chaucer.

That, as a relative pronoun, cannot be governed by a preposition preceding it, but may be governed by one at the end of the sentence which it commences.

The ship that somebody was sailing in.

Sir W. Scott.

In Old English, that was often used with the demonstratives he, his, him, etc., and the two together had the force of a relative pronoun; thus, that he = who; that his = whose; that him = whom.

I saw to-day a corpse yborn to church
That now on Monday last I saw him wirche [work].

Chaucer.

Formerly, that was used, where we now commonly use which, as a relative pronoun with the demonstrative pronoun that as its antecedent.

That that dieth, let it die; and that that is to cut off, let it be cut off.

Zech. xi. 9.

4. As a conjunction, that retains much of its force as a demonstrative pronoun. It is used, specifically: —

(a) To introduce a clause employed as the object of the preceding verb, or as the subject or predicate nominative of a verb.

She tells them 't is a causeless fantasy,
And childish error, that they are afraid.

Shak.

I have shewed before, that a mere possibility to the contrary, can by no means hinder a thing from being highly credible.

Bp. Wilkins.

(b) To introduce, a reason or cause; — equivalent to for that, in that, for the reason that, because.

He does hear me;
And that he does, I weep.

Shak.