Irony/Sarcasm is saying the opposite of what you mean in such a way you can reasonably expect it to be understood as saying the oppostite of what you mean. An ironic or sarcastic work uses irony and sarcasm extensively, or as a major theme. For a work to be ironic or sarcastic does not require that every sentence in the work be ironic or sarcastic.
Carrol seems to think that Swift's "A Modest Proposal" is a counter-example. Yet I don't think you can argue that swift literally means that killing and eating babies is a humane and reasonable proposal. Some of the sentences "Proposal", the facts about how harshly the Irish are treated are meant to be taken literally. But this does not change the fact that the work as a whole is on the sarcasm/irony specturm.
Now to the harder part, separating iron from sarcasm. I do not believe the paraphrasability is a reasonable test. I would say that if you look at statements that are actually taken as irony or sarcasm, the difference is in the degree to which the statement which is to be taken to mean it's opposite is supported. Suppose you say "Charles Manson, one sweet guy". This is sarcasm. The statement is recognizable as meaning the opposite of what the text says almost completely because of knowledge on the part of the reader that Charles Manson is a cruel, psychotic, unrepentant mass murderer. It has been a long time since I read a modest proposal,(Swifts version, not Yoshies) but as I remember it even included statistics about conditions in Ireland; at any rate it included quite a large number of facts. Note that this is a spectrum, not a line. Most sarcasm includes some support. Most irony requires some knowledge on the part of the reader. None the less, I think that this kind of "weight of evidence" type of definition is valid; to the extent that a work provides a great deal of argument for it's position the work is irony. To extent the saying the opposite of what you mean is simply used to say something, rather than provide evidence for it then the statement is sarcasm. Note that the identification of something as being on the irony/sarcasm spectrum is easier than deciding where it lies on the spectrum.I *think* this is a pretty complete definition. However, maybe there is a simple counter-example I have overlooked. -- Gar W. Lipow 815 Dundee RD NW Olympia, WA 98502