slow up/slow down

[sipukka]

how can they mean the same thing?

[theregularme]

It's just like when someone says "I am going up the road" or "down the road" when the road is flat.

It's just something people say.

[Quizmonster]

Usage. For the same reason as 'It's up to you' means the same as 'It's down to you'.

[jno]

in idiomatic expressions, where they don't have physical meanings of 'towards the sky' or 'towards the ground', these little prepositions can be rather unstable. I think 'slow up' and 'it's down to you' are American expressions that have come into British English only fairly recently and are competing with the local versions, though I could be wrong about this.

[mindimplode]

Slow up? Whats down with that? (you see what I did there)

[Quizmonster]

'Slow up' has been in use since the 1880s, J. 'Down to' - in the sense I referred to earlier - is much more recent, having first appeareed around 1970. I don't believe either is an Americanism, however.

[Solon]

Not sure I agree with Quizmonster. Doesn't "it's up to you" mean you are being given a choice whether to do something ot not. Saying "it's down to you" means you are being held responsible for something happening (e.g. the accident was down to you not looking) or you are given an obligation as the only person that can resolve a problem (e.g. it's down to you to get the shopping because I am stuck at work).

[Quizmonster]

You're absolutely right, Solon, in terms of the long-standing use of the phrase 'it's up to you' meaning 'it's your choice'. However, in recent years there is no doubt in my mind that it has taken on the other meaning, too.
In exactly the same way, 'up for' meant 'proposed' as in 'He was put up for a medal in the Falklands conflict.' Alternatively, it might mean 'in town for some purpose', as in 'There are thousands of fans up for the Cup Final.' Nowadays, though, it also means 'ready/available' as in 'She was really up for it!'
Language is in constant flux...it's really as simple as that.

[Kingaroo]

I'm American and I never hear "down to you" used to mean "at your discretion." Only "up to you."

I believe that a lot of english idiioms that use "up" without any connotation of direction are derived from the corresponding phrase in German. Many german verbs use "ab" in the same way we use "up" (clean up, use up, etc.). Unfortunately I cannot substantiate this at all because it has been too many years since my brief exposure to German.