In article <1993Apr16.155919.28040@cs.rochester.edu>, fulk@cs.rochester.edu (Mark Fulk) writes:  |> Flights of fancy, and other irrational approaches, are common.  The crucial |> thing is not to sit around just having fantasies; they aren't of any use |> unless they make you do some experiments.  I've known a lot of scientists |> whose fantasies lead them on to creative work; usually they won't admit |> out loud what the fantasy was, prior to the consumption of a few beers. |>  |> (Simple example: Warren Jelinek noticed an extremely heavy band on a DNA |> electrophoresis gel of human ALU fragments.  He got very excited, hoping that |> he'd seen some essential part of the control mechanism for eukaryotic |> genes.  This fantasy led him to sequence samples of the band and carry out |> binding assays.  The result was a well-conserved, 400 or so bp, sequence  But why do you characterize this as a "flight of fancy" or a "fantasy"? While I am unfamiliar with the scientific context here, it appears obvious that his speculation (for lack of a better or more neutral word) was at least in significant part a consequence of his knowledge of and acceptance of current theory coupled with his observations.  It would appear that something quite rational was going on as he attempted to fit his observation into that theory (or to tailor the theory to cover the observation).  This does not seem like an example of what most would normally call a flight of fancy or a fantasy.  |>  |> It is not clear to me what you mean by rational vs. irrational.  Perhaps |> you can give a few examples of surprising experiments that were tried out |> for perfectly rational reasons, or interesting new theories that were first |> advanced from logical grounds.  The main examples I can think of are from |> modern high-energy physics which is not typical of science as a whole.  Well, I think someone else in this thread was the first to use the word (also, "extra-scientific", etc.).  Nor am I prepared to give a general account of rationality.  In terms of examples, there is some danger of beginning to quibble over what a "surprising" experiment is, what counts as "surprising", etc. The same may be said about "logical grounds".  My point is that quite frequently (perhaps even most frequently) the roots of a new theory can be traced to previously existing theories (or even to previously rejected hypotheses of some other theory or domain).  I would offer some rather well known examples such as Toricelli's Puy de Dome experiment done for the sake of his "sea of air" hypothesis.  Was this theory (and the resulting experimental test) "surprising"? Well, given the *prior* explanations of the phenomena involved it certainly must be counted as so.  Was the theory constructed (and the experiment designed) out of "perfectly rational grounds"?  Well, there was a pretty successful and well know theory of fluids.  The analogy to fluids by Toricelli is explicit. The novelty was in thinking of air as a fluid (but this was *quite* a novelty at the time).  Was the theory interesting?  Yes.  Was it "new"?  Well, one could argue that it was merely the extension of an existing theory to a new domain, but I think this begs certain questions.  We can debate that if you like.