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Identifying things by a single characteristic is not the way abductive inference works in the real world. Someone performing a classification task would use a full set of 'relevant' characteristics in order to identify Socrates as either a man or a cat. Does he have fur, how many legs does he walk on, etc. There would be a rough sense of fitness of the match between the characteristics of the thing and the categories being tested, sometimes expressed as a "distance function" between the thing being tested and the ideal. There might also be a scoring mechanism to put greater weight on certain matches. For instance, a match to 'feathers' would probably have a higher scoring weight than 'skin' - Socrates could only be a a bird.


Abduction is the Great Classifier of reasoning. The phrase "if it looks like a duck and it quacks like a duck then ..." is a classically abductive statement. As attractive as it sounds, this is not a valid mode of reasoning - it is the result of association of characteristics between two subjects, maybe with some practical screening mechanism to improve the chances of success. It is neither a true deduction nor a valid statistical induction about the relationships between the subjects themselves.

Abduction as an Early Warning System

If false deductions are invalid, why do we keep doing it ? We do it because it works well of us, as it has for many millions of years. The old adage, "where there's smoke there must be fire" is a perfect example of a cautionary abductive inference and may provide a hint as to why the abductive mode of inference holds such power over our cognitive processes. It's an early warning system and often a very effective one.



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