Tuesday, 1 April 2014

Key beef

Every once in a while it's time to rail against something that makes no sense, and today is that day.

While trying to determine the identification of a mushroom from Cullaloe I came across this key entry on Roger's mushrooms

Similar things occur in Poland's vegetative key, although the word "usually" is preferred to "normally".

I understand that they are trying to hedge their bets because there's much variation, but in context it makes no sense whatsoever. It betrays a fundamental logical error about how a key is used. Yes, it may be the case that the fruit body is "normally" under 5cm. It may be the case that a leaf is "usually" hairy. However, when you are using a key you are holding in your hand an actual example with an actual size and an actual level of hirsuteness. You cannot, CANNOT determine anything about what it "normally" or "usually" might be.

What you are trying to identify is a real thing, an actual instance, and not a platonic ideal of the species in question. Besides, if you knew what it "usually" or "normally" was like you wouldn't need a key!

So much ink and so much space could have been saved too. Everybody understands that an atypical example may not key out well. If you really, absolutely must, introduce this mushy language into a key, please put in the introduction, "all characters are only what the species usually demonstrates" and then leave it alone.


No comments:

Post a Comment