Generalizing: Sensible Links between S and P

Rule #3: We should consider whether a link between S and P is plausible in light of other knowledge we possess.

To see the point of this rule, consider two contrasting cases. If chemists discovered a new metal, they would determine its melting point in a laboratory, and a single test would be sufficient to support the generalization that all instances of the metal would melt at that temperature. Our theoretical knowledge about physical substances tells us that the melting point of a metal is fixed by its atomic structure, which defines that type of metal.

On the other hand, the generalization that all swans are white was confirmed by countless instances over a long period of time. Yet, this generalization was regarded as somewhat shaky, because biological theory gives us no reason for thinking that all swans must be the same color. Eventually, black swans were indeed discovered in Australia.

Sample size and variety | Disconfirming instances |
Sensible links between S and P

© Copyright 1998, W.W. Norton & Co.