Yes, it’s redundant, but a lot of language is redundant, and it isn’t necessarily useless. We often use redundancy in order to give emphasis, or draw a greater degree of attention to some aspect of the utterance, or to convey affect. Redundancy doesn’t necessarily make language “worse.”
Ending a sentence with a preposition?
That is grammatical heresy, up with which I will not put.
What did you bring me that book to be read to out of from for?
But I would say “I left the key ring in the drawer it was in [rather than some other drawer].” So what about “Leave it in the drawer you found it in”?
“Leave it in the drawer you found it in” would mean don’t take it out of the drawer, to me . “Leave in the same drawer you found it in” would imply to me that the object is removed and replaced, in the same drawer in which it was originally found.
You’re starting off of the wrong foot here, and your subsequent reasoning is wrong because of it.
As mentioned above, this works only if we assume an elision:
It was in the condition in which you found it.
“You found it” is an independent clause and doesn’t state what is intended. Without additional (possibly implied) words, it’s not a modifier of “condition”. You need an adjective phrase for that, e.g., beginning with a preposition.
Best way to say it!
Right. Note your preposition “in”, which makes “in the desk drawer” a modifier. Note that you would not say “Leave it you found it.”
Here’s the grammatical breakdown.
“Leave it.” – the unmodified imperative statement, with implied subject “you”.
“Leave it in a condition.” – “in a condition” modifies the verb.
“Leave it in the condition you found it” – “you found it” modifies “condition”, but it’s not a grammatically correct modifier, since it’s an independent clause.
Leave it in the condition you found it in, sweetheart.
From Li’l Abner:
Put 'em back! The way they was! Oh, put 'em back the way they was!
(Sorry about the mismatched verb.)
From An Officer and a Gentleman:
You put that back where it belongs…