WITTGENSTEIN AND DEFINING CRITERIA

Let us introduce two antithetical terms in order to avoid certain elementary confusions: To the question “How do you know that so-and-so is the case?”, we sometimes answer by giving ‘criteria’ and sometimes by giving ‘symptoms. If medical science calls angina an inflammation caused by a particular bacillus, and we ask in a particular case “Why do you say this man has got angina?” then the answer “I have found the bacillus so-and-so in his blood” gives us the criterion, or what we may call the defining criterion of angina. If on the other hand the answer was, “His throat is inflamed”, this might give us a symptom of angina, I call “sympton” a phenomenon of which experience has taught us that it coincided, in some way or other, with the phenomenon which is our defining criterion, Then to say “A man has angina if this bacillus is found in him” is a tautology or it is a loose way of stating the definition of “angina”. But to say, “A man has angina whenever he has an inflamed throat” is to make a hypothesis. (BB, pp. 24–25)¹