It goes without saying that idiomatic phrases can make some people crazy. Take it goes without saying. According to the logical purist, if something truly "goes without saying," then why would a speaker or writer point it out? Why, indeed.

A translation of the French cela va sans dire, the English it goes without saying has been part of our language since 1878. Folks who keep track of such phrases note it has kin in the expressions needless to say and I don't need to tell you. But again, if something truly need not be said, why say it? And if it does need to be said, why claim it doesn't?

Our response to all this is that applying logic to idiomatic expressions is just illogical. These idioms fulfill two important communication needs. First, all these phrases can emphasize that the writer or speaker regards the statement being made as in some way self-evident. And second, when used for that emphasis, the expressions can make a graceful transition between sentences, paragraphs, or thoughts. At times, they can also be used to apply a sly rhetorical flourish, as when the politician says, "It goes without saying that my opponent is an inveterate liar and a horse thief."