Logical determinism

Logical determinism is an old philosophical position that holds that "because propositions about future events are true or false even before the events occur, the events that the true propositions refer to must happen necessarily." It seems absurd that the truth of a statement can entail future events, but nailing down exactly what is wrong with logical determinism has occupied much discussion.

An extended analysis was made by Freddoso in 1983. Freddoso provides an analysis of the example statement about the future that "Katie will wash her car at time T". Several preliminaries are needed. One is the description of the truth of historical fact. Such a statement refers to things that cannot be changed, but are only accidentally true, that is, might not have been true, and in fact were not true at some earlier time. An example is a statement made today that Socrates drank hemlock, which is true today and in fact has been true ever after the event, but was a false statement when Socrates was a boy. This kind of truth that applies to a statement about the past after an event happens is called accidental necessity, or necessity per accidens. The truth of such statements is temporally contingent, that is, the truth of the statement depends upon the time frame under discussion. This idea of the unalterable nature of truth following a contingency is generalized formally to arbitrary times t as statement C below:

(C) If p is true at t (for example, some past time t), then the proposition that p was the case is necessary per accidens at every moment after t, and the proposition that p was never the case is impossible per accidens at every moment after t.

This statement about p can be extended to statements q that are implied by p, as expressed formally below:

(B) If p entails q, and p is necessary per accidens at t, then no one has the power at or after t to bring it about that q is or will be false.

The argument for determinism then runs as follows:

(P1) The proposition: "Katie will wash her car at T" is true now, a time long before T. (assumption)

(P2) So the proposition: "Katie will wash her car at T" will be necessary per accidens at every future moment, including every moment subsequent to now that precedes or is identical with T. (from (P1)and (C))

(P3) The truth of the proposition: "Katie will wash her car at T" entails that if the time is T, then Katie is washing her car. (assumption)

(P4) Therefore, no one (including Katie) will have the power at or before T to bring it about that it is or will be false that if T is present, then Katie is washing her car. That is, no one will have the power at or before T to bring it about that it is or will be true that Katie is not washing her car when T is present. (from (P2), (P3), and (B))

Freddoso then examines challenges to the various propositions above. He attributes to Aristotle the view that truth or falsity is not even a property of statements about the future, which neither are true nor false before the event. However, Freddoso supports as most plausible the objection, called the Ockhamistic objection, that the truth of p before an event occurs is established only after the event occurs, and while the early future tense statement can be true, that truth is only back-propagated from the time of the event. Backmann calls this the Ockhamist's claim of primacy of the present. Consequently, the truth of the statement: "Katie will wash her car at T" does not depend upon the truth of this statement before Katie washed her car.

Different objections have been raised. Backmann refers to Swartz, and to Keil as suggesting logical determinism confuses semantic with causal necessity. Swartz argues that it is difficult to assign a particular instant when the truth value of a contingent statement changes, and finds it unpalatable that an abstraction like a proposition about the future should be mired in such minutiae.