An example of common sense reasoning: “For sale: baby shoes, never worn.”

Yesterday day I had a short post about the difference between a narrative and a narrative that is also a story. One of my examples was a statement that’s been circulating as a meme for some time now: “For sale: baby shoes, never worn.” Strictly speaking that’s not a story nor even a narrative. It’s a statement that something is for sale, namely baby shoes that have never been worn. However the statement is of such a nature that we can easily infer a story that led to that statement. That inference is an example of common sense reasoning as the concept is understood in artificial intelligence and computational linguistics.

Why common sense? Because no special knowledge is required. Anyone growing up under the appropriate circumstances will possess the knowledge required to infer such a story.

First, one must recognize that it is advertising something for sale. The words, “for sale,” could simply be a statement of fact. But we recognize that such a statement is also an offer, “something is being offered for sale.” The fact that that inference is utterly trivial doesn’t negate the fact that an inference is required to go from the statement of act to the offer. However, if one sees that statement in a newspaper in the appropriate section, its presence in that section constitutes the offer.

Now, just what story are we inferring from the statement? The most likely story is that a couple bought the shoes in anticipation of the birth of a child. The infant died shortly after birth, making the baby shoes useless. Hence they are available for sale, never having been worn.

All of that has to be inferred, the inferences are trivial, but still, they are inferences. Let’s tease things apart. Here’s one possibility:

1. When an infant is expected, preparations must be made.
2. Preparations include buying clothing.
3. Shoes are an item of clothing.
4. Once the infant is born, the items of clothing will be used.
5. If however the infant is stillborn, or dies after birth, the items of clothing will not be worn.
6. In that case something must be done with those items.
7. They could be put up for sale.
8. That would lead to placing an advertisement in a newspaper.
9. The statement “For sale: baby shoes, never worn” is such an advertisement.

You could imagine other circumstances, but that seems to me the most likely case. But whatever alternative circumstances you propose, the point is that they must be inferred from the statement. They are not explicit in it. Ordinary language requires scads of such inferences. That requirement is the problem of common sense knowledge as it exists in artificial intelligence.