(These are excerpts from my book "Intelligence is not Artificial")
Another Failure: Common Sense
Common sense, besides learning, was another missing ingredient. Humans employ naturally several forms of inference that are not deduction, and therefore are not exact. In general, we specialize in "plausible reasoning", not the "exact reasoning" of mathematicians. Finding exact solutions to problems is often pointless: it would take too long. If a tiger attacks you, you don't start calculating the most efficient trajectory: you would be dead by the time you finished your calculations. This became a popular subject of research after the publication of "Plausible Reasoning" (1976) by the German-born philosopher Nicholas Rescher at the University of Pittsburgh and of "Logic and Conversation" (1975) by the British-born philosopher Paul Grice at UC Berkeley.
Most of our statements are actually uncertain. "The sky is blue" is obviously just an approximation; so is "blood is red". My height is actually not 171 cm: it is probably something like 171.46234782673... cm. Hence in 1965 the Azerbaijani-born mathematician Lofti Zadeh invented Fuzzy Logic at UC Berkeley.
In classical logic an entity either belongs or doesn't belong to a set. In fuzzy logic an entity has a degree of membership in a set. I belong to both the set of tall people (to some degree) and to the set of short people (to some degree). Following Zadeh's classic paper "Outline of a new approach to the analysis of complex systems and decision processes" (1973), a number of mathematicians invented "fuzzy inference systems": Ebrahim "Abe" Mamdani at University of London in 1975, Yahachiro Tsukamoto at the Tokyo Institute of Technology in 1979, Michio Sugeno at the Tokyo Institute of Technology in 1985.
Almost everything we say has a margin of uncertainty and approximation. Even if we don't know Bayes' theorem, we use probabilities all the time (and in most cases it is not the "probability" that mathematicians use). We unconsciously side with the French physicist Pierre Duhem: the certainty that a proposition is true decreases with any increase of its precision. I am certain of being 171 cms high until you ask me to be more precise: then i am less certain whether i am 171.1 cms high or 171.2 or 171.3 or...
We are also very good at changing our conclusions: if you made plans to have dinner at a restaurant and it turns out that the restaurant has gone out of business, you effortlessly change your plans. Hence in 1979 Drew McDermott at Yale University worked out "Nonmonotonic Logic" and John McCarthy at Stanford published "Circumscription".
We normally deal with objects, not with elementary particles or waves. The world that we encounter in our daily lives is a world of objects, and we intuitively know how to operate with objects. For example, water can certainly have all sorts of temperatures, but the important thing is that at a certain temperature it freezes and at a certain temperature it boils. We deal with "qualities" (such as "hot" and "cold") rather than with quantities (such as 32.6 degrees Celsius and -4 degrees Celsius). And these "qualities" are "fuzzy": my height is both short and tall, depending on the people around me. To some extent i am short and to some extent i am tall. There other simple laws of causality connecting our actions and our objects that don't require any knowledge of theoretical Physics. Hence Pat Hayes in Britain published the "Naive Physics Manifesto" (1978), and "qualitative reasoning" was pioneered by two theses published at the MIT, first Johan DeKleer ("Causal and Teleological Reasoning in Circuit Recognition", 1979), who had worked on the Sophie project with Brown and Burton at BBN, and then Kenneth Forbus ("Qualitative Reasoning about Physical Processes", 1981). In 1984 Doug Lenat started the project Cyc to catalog commonsense knowledge. (I have written a lengthy survey of these commonsense theories in my other book
"Thinking about Thought").
There was a sense that "intelligence" without common sense is not intelligence, or, worse, it is plain dangerous. I would add that a sign of common sense is the other sense, the sense of humor. Machines can't laugh.
"A black cat crossing your path signifies that the animal is going somewhere" (Groucho Marx).
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