Possibility and Impossibility

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JOURNAL OF METAPSYCHOLOGY 431 Burgess Drive, Menlo Park, California 94025

Article 61
October 13, 1990

Possibility and Impossibility

We often speak of things being possible or impossible, but there are different kinds of possibility and impossibility:

Conceptual
Logical
Empirical

Central to the concept of possibility, probability, and impossibility is the concept of a "truth value", given here in person-centered terms:

Definition: The truth value (of a concept) is the degree to which (that concept) is accepted by a person.

Obviously, two or more different people may assign different truth values to the same concept. I may think UFO's exist; you may think they do not. But from a person-centered viewpoint (the point of view of one person at one particular time), each concept, if it has a truth value at all, can have only one. By "truth value", I mean the same thing as "degree of reality", "degree of actuality", "degree of assent", or "degree of existence".

Following computer custom and probability theory, we will define a truth value of 0 as "completely false" and a truth value of 1 as "completely true". Truth values in between 0 and 1 correspond to various probabilities or degrees of reality, belief, or assent in between a total yes and a total no.

Possible / Impossible

Let's talk about possibilities first. A concept is possible if it cannot be assigned a truth value of 0; it is impossible if it must be assigned a truth value of 0.

More specifically, each of the following types of possibility has the prior types as a prerequisite. Thus something must be a conceptual possibility in order to be a logical possibility and must be a conceptual and a logical possibility to be an empirical possibility.

Conceptual Possibility / Impossibility

Something is conceptually possible if it is meaningful, i.e., if it is truly a concept. In other words, something is conceptually possible if it can be assigned a truth value. Something that makes no sense whatsoever is a conceptual impossibility or meaningless and cannot be assigned a truth value.

Logical Possibility / Impossibility

A concept is logically possible if it cannot be assigned a truth value of 0 without reference to experiential data. The concept of a unicorn is logically possible. A logical impossibility is a concept that can be assigned a truth value of 0 without reference to experiential data. The concept "the cat is on the mat and the cat is not on the mat" is meaningful but false without reference to experience, hence a logical impossibility.

Empirical Possibility / Impossibility

A concept is empirically possible if it cannot be assigned a truth value of 0, even with reference to experiential data. It is empirically impossible if it has a truth value of zero when experiential data is taken into account.

Potential / Actual

A concept is potential if it might be assigned a truth value of 1. It is actual if it has been assigned a truth value of 1.

Fictional / Factual

A concept is fictional if it has been assigned a truth value of 0; it is factual if it has been assigned a truth value of 1.

Probable / Improbable

A concept is probable if it has a truth value between 0.5 and 1; a concept is improbable if it has a truth value between 0.5 and 0. All probabilities are empirical possibilities.

Betting as a Measure of Probability

You can get a rough idea of the degree of probability a person assigns to something by finding out what sorts of odds that person would give in a bet on the subject. For instance, if he would give two to one odds that a certain team will win a football game, he will have assigned approximately a 66% probability to that team's winning.

How Certain is Certain?

Often we say we are certain of something when in fact we have assigned only a high probability to it. I am certain that I will go home from work today, although I recognize the remote possibility that I might die or spend the night at work for some reason. A probability becomes a certainty at the point at which a person is willing to act on it. A certainty is a high enough degree of probability to justify action.¹

Frank A. Gerbode, M.D.
Director, IRM

¹ See also JOM Article 39 "Quasi-Entities" for more on this topic.

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