Actually the premise is "the market is overvalued and therefore there will be a significant correction."
Technically the current value is the correct value. The question isn't whether this value is "wrong" - it isn't, by definition - but whether or not Mr Market is delusional and prices will crash at some point in the near/mid future.
Explicitly, the distinction is between investors who are looking at fundamentals, and investors who are looking at market momentum and trying to factor in their guesses about politics and Fed policy.
If you consider fundamentals, P/E is up to insane levels in a barely functioning economy. If you consider politics - optimism may be justified. Possibly.
But if it is - what does that say about the value stock markets are supposed to provide?
