ANALOGY
What is analogy?
"Analogy" is a technical term, defined by Webster's New World Dictionary as meaning similarity in some ways, [with] the inference that certain resemblances imply further similarity. The concise way to say this, is that things are "somewhat similar" - but that immediately raises complications. On what basis must things be similar, and to what extent must they be similar in order to qualify as analogous? Given that analogies are widely used, but just as widely criticized, it therefore becomes important to be clear about what they are. What "analogous" identifies, is the sharing of certain functional similarities, which means that the members of this category resemble each other regarding certain features or patterns, but do not necessarily have the same structure or mechanism.
One of the rules of traditional logic was that of "the excluded middle" - either something was "right" or it was "wrong", it was "sacred" or it was "secular", etc. Regrettably, this was not a very accurate description of much of reality, but the practice persisted for centuries. The criticism that arose about this practice likened it to the "Procrustean Bed" in the ancient Greek story about travelers who were offered "one size fits all" sleeping accommodations, and those not of a precise stature were either "cut down to size" or "stretched on the rack" to lengthen them up. This two- valued approach to logic, the "either-or" approach, was fine and well for theorists, but practical people had to live with much more uncertainty - most things were neither black nor white, but rather shades of gray. Philosophy finally caught up with these practical concerns when "pragmatism" was developed in the United States (Dewey, 1929) and "practical reason" in Europe (De Bono, 1973). It is not necessary to assume or demand that everything sort neatly into homologous or dichotomous categories - in reality boundaries often shade off into one another so that something may qualify "more or less" for inclusion or exclusion depending on how the lines are drawn. In real life, most people think this way intuitively all the time anyway. This does NOT imply that "anything goes" but rather allows diversity to be accommodated in analysis.
How is analogy used?
By analogy, computer information storage is metaphorically called "memory", but computer "memories" are not based on the same components as biological memories, nor do they operate in the same way. There is, however, enough resemblance that the analogy is retained. Criticisms about analogies arise from "purists" who want to insist that descriptions should preserve a degree of technical exactness which would preclude using "free and loose" terminology (i.e., analogies) to make questionable comparisons. The appropriate reply is that for some purposes such analogies are quite suitable and very convenient, so long as the user doesn't forget that such categories are based on appearance rather than equivalence.
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