THE INTENSION-EXTENSION DISTINCTION

seddon's picture
Submitted by seddon on Fri, 2013-06-14 17:14

In another post, I mentioned the distinction between the intension and extension. On pp. 104-6 of ITOE, Peikoff mentions and dismisses this dichotomy as “another artificial split . . . between an existent and its characteristics.” (105) He quotes Ruby’s LOGIC: AN INTRODUCTION to introduce the distinction: “The intension of a term, . . .is what is usually called its definition. The extension . . .simply refers us to the set of objects to which the definition applies . . .Extension and intension are thus intimately related, but they refer to objects in different ways—extension to a listing of the individuals who fall within its quantitative scope, intension to the qualities or characteristics of the individuals.” (90 & 91)
Reading this quotation before looking at Peikoff’s objection, one might wonder What’s the problem? Take intension or definition first. Rand certainly thought definition important, she devoted chapter V of ITOE to this issue. Take extension second. Rand often reminds us that the meaning of a concept is its referents. What’s the problem?

Consider the history of this distinction. It goes back to the father of definition, Plato. Think of the MENO where Socrates asks Meno for a definition (the intension) of virtue and Meno misunderstands what is needed and keeps giving examples (referents or extension) of virtue.

Aristotle, on the other hand, referring to the MENO takes Meno’s side. (POLITICS, I, 13, 1260a20-28. History has decided that they are both right. Here is H. W. B. Joseph’s considered opinion: “Sometimes we are more interested in the one [intension], sometimes the other [extension]. ” LOGIC: AN INTRODUCTION (142) Rand would seem to agree. Sometimes she is interested in intension or definition, e.g., ch. 5 of ITOE. Sometimes she is interested in the other, e.g., when she states that the meaning of a concept is its referents or extension.

Given this, what is Peikoff’s complaint? He complains that the theory introduces “an artificial split between an existent and its characteristics.” (105) Really? If you ask me for an example of a novelist and I name Ayn Rand, would you accuse me of introducing “an artificial split between an existent and its characteristics”? You asked for an example and I gave one.

Now let’s say you asked for the definition of man and I said, “a rational animal.” Would you bitch at me for separating a definition from the existent.

He then complains that, “One’s choice, in effect, is: either to mean existents, apart from their characteristics [this definitely misconstrues the distinction]---or (certain) characteristics, apart from the existents which possess them.”

How misleading is his use of “certain.” The characteristics used in a definition give the essence of the existents being defined; they’re not just “certain” characteristics. As Kelley writes in his Logic text, a definition “should state the essential attributes of a concept’s referents.” (44) Joseph (111) and Ruby (105) agree. How is this a separation of existents from its characteristics? Intension and extension do different jobs. Surely Joseph has it right here; “Sometimes we are more interested in the one [intension], sometimes the other [extension].”

Now that is Peikoff’s whole “argument.” I find it less than convincing. And to the extent that it is used in his attack on the analytic-synthetic distinction, then that attack is weakened.

Bottom line. If you agree that we can both define a term and give an example of it, then you buy the intension-extension distinction.

Fred


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Personal note

seddon's picture

For those interested, Kelley does not include the distinction in his Logic book. Here is what he says in full:

"I do not discuss . . . the intension/extension distinction a) because I oppose it on philosophical grounds, and b) because I do not think it would have great pedagogical value even if true. Those who disagree, however, can easily introduce it within the framework established by the chapters on classification and definition." INSTRUCTOR'S MANUAL THE ART OF REASONING, 1st ed. p. 20
I taught Kelley's text for over 20 years and never used the distinction.

Fred

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