A logical statement is one that conforms to one of a variety of rules that are used to extrapolate from an axiom or premise. Logical is in no way a synonym for true or even unemotional thought. For example, take the following logical argument.
  • If a voice in my head tells me to do something, then I am receiving a command from God (If A, then B)
  • If I receive a command from God, then I must do what it says. (If B, then C)
  • A voice in my head tells me to kill people. (A)
  • Therefore: I must do what it says. (C)
This is a logically valid statement, but it is probably not true. My high-school logic teacher (yes, I was lucky) used arguments based on the premise "Cher is a dog" to illustrate this point in less graphic ways.

An often unstressted connotation of the word "logical" and "logic" is the non-classicist notion of logic. For example, it makes sense to speak of a "Marxist logic", a "psychoanalytic logic", or a "Republican logic". However, the definitions offered above do not stress even the possibility of these phrases making sense, as does the very common practice in our society of confusing logic with an Aristotelian or classical conception of logic as the specific system of dialectical reasoning in which argumentative forms such as modus tollens and modus ponens serve as rhetorical exemplars.

For example, modus ponens is represented in the following familiar rule of inference: if P then Q, P, therefore Q. According to the classical conception of logic, any system of reasoning that does not progress according to this rule can safely be said to be illogical.

This, however, isn't exactly fair given that logicality is not defined as any particular system of reasoning, but rather the broad and vague concept of a system of reasoning as in the Greek word logos, which could be translated as logic or reason or rational system of thought, from which our English "logical" is derived.

If we read Freud, for example, we can see that he stresses a great variety of progressions of thought in which a trope such as modus ponens is not exemplified. For example, Freud's notions of sublimation and repression make it possible to think ratioanlly (scientifically) in a form that could be represented as: if P then Q, P, not Q. As in the case of the familiar Freudian trick of arguing from the denial of a statement to the assertion of its content. For example: the patient recounts a dream, the analyst asks the patient if the dream means "Q", the patient denies it, and the analyst takes this as proof that it does. According to Freud, this is not an irrational movement of thought. It was part of Freud's claim that such a system of thought is systematically present in human psychical activity and is logical.

To say that Freud (or Marx, or Hegel, or Derrida, or postmodern thinkers) is illogical is to ambiguously state that Freud proferred systems of thought that are not covered by the classical logic (as described by Aristotle, Plato, analytic philosophers, et. al.). This does not mean that he proferred illogicality. What Freud offered was certainly a systematic representation of thinking with its own assumptions, axioms, and rules of inference. It is not, then, by definition illogical.

logic bomb = L = loop through

logical adj.

[from the technical term `logical device', wherein a physical device is referred to by an arbitrary `logical' name] Having the role of. If a person (say, Les Earnest at SAIL) who had long held a certain post left and were replaced, the replacement would for a while be known as the `logical' Les Earnest. (This does not imply any judgment on the replacement.) Compare virtual.

At Stanford, `logical' compass directions denote a coordinate system relative to El Camino Real, in which `logical north' is always toward San Francisco and `logical south' is always toward San Jose-in spite of the fact that El Camino Real runs physical north/south near San Francisco, physical east/west near San Jose, and along a curve everywhere in between. (The best rule of thumb here is that, by definition, El Camino Real always runs logical north-south.)

In giving directions, one might say: "To get to Rincon Tarasco restaurant, get onto El Camino Bignum going logical north." Using the word `logical' helps to prevent the recipient from worrying about that the fact that the sun is setting almost directly in front of him. The concept is reinforced by North American highways which are almost, but not quite, consistently labeled with logical rather than physical directions. A similar situation exists at MIT: Route 128 (famous for the electronics industry that grew up along it) wraps roughly 3 quarters around Boston at a radius of 10 miles, terminating near the coastline at each end. It would be most precise to describe the two directions along this highway as `clockwise' and `counterclockwise', but the road signs all say "north" and "south", respectively. A hacker might describe these directions as `logical north' and `logical south', to indicate that they are conventional directions not corresponding to the usual denotation for those words.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

Log"ic*al (?), a. [Cf. F. logique, L. logicus, Gr. .]


Of or pertaining to logic; used in logic; as, logical subtilties.



According to the rules of logic; as, a logical argument or inference; the reasoning is logical.



Skilled in logic; versed in the art of thinking and reasoning; as, he is a logical thinker.



© Webster 1913.

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