My source told me that we cannot say "He is not the man who he was" for the following reasons.
1. "The man" in "He is not the man he was" means "the kind of man" or "the entity" or "the being."
2. "Man" in that sentence is "neuter, not having all the attributes of a person (more like an adjective in a way)."
3. We can use "that," which "is not marked as either personal or impersonal."
4. The use of "who" would be "semantically absurd."
Many thanks to TheParser for sharing that compelling analysis, which is probably as "on the money" as the source's credentials would suggest it is. That said, I have been thinking hard about the construction and should like humbly to propose an alternate analysis of its ill-formedness with
who.
I think the
(that)-clause in
He is not the man (that) he was can, and perhaps should, be analyzed as a comparative clause rather than a relative clause. I analyze it as comparative construction of degree/extent, with
He is not the man (that) he was having the meaning
He is not a man to the (same) extent that he was.
This analysis changes the source of the semantic absurdity of
who. The use of
who would be as absurd as its use in
*[strike]
He is not a man to the extent who he was[/strike]. This result applies to other relative pronouns, even
which. For example:
(i) Felix isn't the cat (that) he was five years ago.
(ii) *? Felix isn't the cat which he was five years ago.
As support for this analysis, I shall draw upon what I deem to be two related constructions: one with
half the, the other with
twice the. In each construction, the extent of identity, or lack thereof, is specified. Consider the following examples:
(iii) Felix isn't half the cat (that) he was five years ago.
(iv) *? Felix isn't half the cat which he was five years ago.
(v) Felix was twice the cat (that) he is now five years ago.
(vi) *?! Felix was twice the cat which he is now five years ago.
As further support for this analysis, I should like to point out that the
(that)-clause, which, again, I am proposing is a comparative clause of degree/extent rather than a relative clause, can take a different subject from the subject of the superordinate clause:
(vii) I am not (nearly) the man that Gandhi was.
(viii) *?! I am not (nearly) the man who Gandhi was.
(ix) Felix isn't half the cat that Garfield was.
(x) *?! Felix isn't half the cat which Garfield was.
