Why do people say "to be honest"?
For quite some time, I've been hearing the phrase "to be honest" almost every day. I've heard friends say it, characters on TV shows, and even an NPR reporter said it in an interview.
Example:
"To be honest, I don't like spaghetti."
Why do people have to specify when they are being honest? Or I've thought maybe the phrase is actually supposed to mean "to be blunt" or "let me tell it to you straight."
How did the word "honest" get in the mix?
"To be honest" is an example of an adverbial disjunct, which indicates the speaker's attitude toward the sentence without affecting the meaning of the sentence. It is often used, consciously or otherwise, to preface a statement that the speaker believes is particularly candid in the present context, possibly to an extent that might cause mild offense.
It's a bit of a set phrase these days, and as is usually the case with set phrases, it's best not to parse it too closely in casual use.
In addition to phenry's answer, these meaningless "to be honest" additions might also be considered a discourse marker: http://en.wikipedia.org/wiki/Discourse_marker
In linguistics, a discourse marker is a word or phrase that is relatively syntax-independent and does not change the truth conditional meaning of the sentence, and has a somewhat empty meaning. Examples of discourse markers include the particles "oh", "well", "now", "then", "you know", and "I mean", and the connectives "so", "because", "and", "but", and "or".
Common discourse markers used in the English language include "you know", "actually", "basically", "like", "I mean", "okay" and "so".
In many cases, claims of veracity are used by liars to discourage the listener from considering the possibility that what follows may be untrue. In the spaghetti example, though, I believe the intended meaning of the disclaimer is probably closer to "I am aware that proper decorum would imply that a guest should always be appreciative of the food offered by the host, but would nonetheless like you to know that I cannot receive from your spaghetti a level of enjoyment commensurate with the effort you spend preparing it." Basically, the purpose of the statement would be to avoid a situation where a host might mistake a guest's gracious acceptance of something as an indication that the guest would like the host to serve it in future.
The subfield of linguistics called pragmatics deals with this kind of topic. It might be a sort of "hedging" to make what follows more polite—a semi-apology without changing its contents.