McGrath of Harlow said:

My finger slipped in my last post - what I meant to say was that with irr being an eroded in, "irrecognizable" is really a way of writing "inrecognizable."

(And I suppose the dash in that last sentence could be seen as taking the place of a semicolon. Couldn't have been a comma - I suppose it could have been a full stop, at a stretch. I prefer a dash. Looks better on the page.) If you look, there is NO dash in either of those quoted paragraph. What is there in each case is a hyphen with spaces before and after. A dash in printing (referred to as an em dash) is a longer horizontal bar than a hyphen, and is neither led nor followed by a space. In typing, the long dash bar is rendered as two hyphens, with no spaces before or after.

The function of the hyphen is to join two words or word parts into one expression, as in "a dark-green color". The function of the dash, on the other hand, is to separate sections of a sentence--sometimes as a parenthetical indicator, sometimes to indicate a breaking off of a thought.

Dave Oesterreich