*That or when.*—"Men walking (that walk, or when they walk) on ice sometimes fall."
It is better to use "men walking" to mean "men when they walk." If the relative is meant, use "men that walk," instead of the participle.
(1) "While he was } Walking on { (1) the road, } he fell." (2) "Because he was } { (2) the ice, }
When the participle precedes the subject, it generally implies a cause: "Seeing this, he retired." Otherwise it generally has its proper participial meaning, e.g. "He retired, keeping his face towards us." If there is any ambiguity, write "on seeing,"—"at the same time, or while, keeping."
(1) "Though he was} {(1) he nevertheless stood
} { his ground."
(2) "Since he was } Struck with terror, {(2) he rapidly retreated."
(3) "If he is } {(3) he will soon retreat."
*8. When using the Relative Pronoun, use "who" and "which" where the meaning is "and he, it, &c.," "for he, it, &c." In other cases use "that," if euphony allows.*
"I heard this from the inspector, who (and he) heard it from the guard that travelled with the train."
"Fetch me (all) the books that lie on the table, and also the pamphlets, which (and these) you will find on the floor."
An adherence to this rule would remove much ambiguity. Thus: "There was a public-house next door, which was a great nuisance," means "and this (i.e. the fact of its being next door) was a great nuisance;" whereas that would have meant "Next door was a public-house that (i.e. the public-house) was a great nuisance." *"Who," "which," &c. introduce a new fact about the antecedent, whereas "that" introduces something without which the antecedent is incomplete or undefined.* Thus, in the first example above, "inspector" is complete in itself, and "who" introduces a new fact about him; "guard" is incomplete, and requires "that travelled with the train" to complete the meaning.
It is not, and cannot be, maintained that this rule, though observed in Elizabethan English, is observed by our best modern authors. (Probably a general impression that "that" cannot be used to refer to persons has assisted "who" in supplanting "that" as a relative.) But the convenience of the rule is so great that beginners in composition may with advantage adhere to the rule. The following are some of the cases where who and which are mostly used, contrary to the rule, instead of that.