It may seem to the reader that a rule with so many exceptions to it is not worth observing. We would remind him (i) that it is based upon those palpable misuses of the relatives about which every one is agreed; (ii) that of the exceptions the first and last result from, and might disappear with, the encroachment of 'who' and the general vagueness about the relatives; while the other two, being obvious and clearly defined, do not interfere with the remaining uses of 'that'; (iii) that if we are to be at the expense of maintaining two different relatives, we may as well give each of them definite work to do.
In the following subsections we shall not often allude to the distinction here laid down. The reader will find that our rules are quite as often violated as observed; and may perhaps conclude that if the vital difference between a defining and a non-defining clause were consistently marked, wherever it is possible, by a discriminating use of 'that' and 'which', false coordination and other mishandlings of the relatives would be less common than they are.
c. 'And who'; 'and which '.
The various possibilities of relative coordination, right and wrong, may be thus stated: (i) a relative clause may be rightly or wrongly coordinated with another relative clause; this we shall call 'open' coordination; (ii) it may be rightly or wrongly coordinated with words that are equivalent to a relative clause, and for which a relative clause can be substituted; 'latent' coordination; (iii) a clause that has obviously no coordinate, open or latent, may yet be introduced by 'and' or other word implying coordination; for such offenders, which cannot be coordinate and will not be subordinate, 'insubordination' is not too harsh a term.
The following are ordinary types of the three classes:
(i) Men who are ambitious, and whose ambition has never been thwarted,...
Pitt, who was ambitious, but whose ambition was qualified by...
