Lillian had gathered some very pretty purple geranium flowers from a bush in the yard at the farm. She was holding the flowers and noticed a purple petal on the table.
“Must be from the flower!” she said.
Background: The philosopher CS Pierce is well-known for insisting that in addition to the traditional categories of deductive reasoning and inductive reasoning, there is another category he called abductive reasoning. The three-way distinction among these kinds of reasoning is now widely accepted and often illustrated as follows:
- Deductive. Suppose you have a bag of red marbles. You draw one from the bag. You can infer by deduction that it is red.
- Inductive. Suppose you have a bag of marbles of unknown colour. You draw one from the bag. You can infer by (weak) induction that the marbles in the bag are red.
- Abductive. Suppose you have a bag of red marbles. You notice a red marble lying near the bag. You can infer by abduction that it is from the bag.
Since I had lectured at Melbourne Uni on this distinction, and used this way of illustrating it, a month or two ago, Lillian’s inference stood out as perfectly analogous to the classic illustration of the abductive inference.
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