|Using relative pronouns|
from Nigeria asks:
In practice, I would say: 'The girl you described as smart has failed the exam', but that's because I'm not sure if I should use 'who' or 'whom'.
There are two possibilities. In formal English we would say, or, especially, write: 'The girl whom you described as smart has failed the exam.' Whom always denotes the object of a verb and would be replaced by 'her' if we were to split this sentence into two separate sentences: 'The girl has failed the exam. And yet you described her as smart.' (Note that 'smart' = 'clever' in this context.)
In conversational English, 'in practice' as you say, the relative pronoun would normally be left out completely: 'The girl you described as smart has failed the exam.' (You will also in speech find people saying: 'The girl who you described as smart has failed the exam', although this is not grammatically accurate or formally correct.)
of the relative pronoun whom is particularly common when the
verb is linked to a preposition. Compare the following 'defining'
course, if who is the subject, rather than the object, of the
relative clause, or if the relative clause is 'non-defining', i.e.
used to convey non-essential information, who cannot be omitted.
We cannot say:
is one other possible relative pronoun which we could use with the
'friend I went out with' sentences and that is that which is
often an alternative for 'whom', 'who' and 'which'. That is
very versatile because it can refer to people or things and can be
used as the subject or object of a relative clause. Compare the following: