Logical necessity,physical necessity,ethics, and quantifiers

Some philosophers, for example Quine, doubt the possibility of jointly using modalities and quantification. Simple model‐theoretic considerations, however, lead to a reconciliation of quantifiers with such modal concepts as logical, physical, and ethical necessity, and suggest a general class of modalities of which these are instances. A simple axiom system, analogous to the Lewis systems S1 —S5, is considered in connection with this class of modalities. The system proves to be complete, and its class of theorems decidable.     

Supervenience and causal necessity

Causal necessity typically receives only oblique attention. Causal relations, laws of nature, counterfactual conditionals, or dispositions are usually the immediate subject(s) of interest. All of these, however, have a common feature. In some way, they involve the causal modality, some form of natural or physical necessity. In this paper, causal necessity is discussed with the purpose of determining whether a completely general empiricist theory can account for the causal in terms of the noncausal. Based on an examination of causal relations, laws of nature, counterfactual conditionals, and dispositions, it is argued that no reductive program devoid of essentialist commitments can account for all the phenomena that involve causal necessity. Hence, neo-Humean empiricism fails to provide a framework adequate for understanding causal necessity.I am grateful to D. M. Armstrong, Ellery Eels, Kit Fine, Philip Quinn, Elliot Sober, Chris Swoyer, Bas van Fraassen, and an anonymous Synthese referee for helpful comments on an earlier draft of this paper.     

Knowledge and epistemic necessity

Claims of the form ??I know P and it might be that not-P?? tend to sound odd. One natural explanation of this oddity is that the conjuncts are semantically incompatible: in its core epistemic use, ??Might P?? is true in a speaker??s mouth only if the speaker does not know that not-P. In this paper I defend this view against an alternative proposal that has been advocated by Trent Dougherty and Patrick Rysiew and elaborated upon in Jeremy Fantl and Matthew McGrath??s recent Knowledge in an Uncertain World.     

Wittgenstein and logical necessity

An attempt is made to show that Wittgenstein's later philosophy of logic is not the kind of conventionalism which is often ascribed to him. On the contrary, Wittgenstein gives expression to a “mixed” theory which is not only interesting but tends to resolve the perplexities usually associated with the question of the a priori character of logical truth. I try to show that Wittgenstein is better understood not as denying that there are such things as “logical rules” nor as denying that the results of applying such rules are “logically necessary,” but as trying to understand what it is to appeal to a logical rule and what it means to say that the results of applying such a rule are “necessary.” He is not so much overthrowing standard accounts of logical necessity as discovering the limits of the concept.     

Temporal necessity and the conditional

In [12] Richmond Thomason and Anil Gupta investigate a semantics for conditional logic that combines the ideas of [8] and [9] with a branching time model of tense logic. The resulting branching time semantics for the conditional is intended to capture the logical relationship between temporal necessity and the conditional. The central principle of this logical relationship is Past Predominance, according to which past similarities and differences take priority over future similarities and differences in determining the comparative similarity of alternative possible histories with respect to a given present moment.In this paper I will use ordinary possible worlds semantics (i.e. Kripke frames) to solve the completeness problem for a system of logic that combines conditional logic with temporal necessity in the context of Past Predominance. Branching time models turn out not to be necessary for the articulation of Past Predominance, and this means that one can axiomatize Past Predominance without first having to solve a much more difficult problem: the completeness problem for the logic of temporal necessity in the context of branching time.Thomason and Gupta argue in [12] that in addition to Past Predominance, temporal necessity and the conditional are logically related, by what have become known as the Edelberg Inferences, whose apparent validity motivates the very complicated theory presented at the end of [12]. I will conclude this paper by examining how the Edelberg inferences would be incorporated into the possible worlds based system presented in the earlier sections of this paper.This article is based on the second chapter of my doctoral dissertation Studies in the Semantics of Modality, University of Pittsburgh, 1985. I thank my adviser Richmond Thomason for his patient help throughout the course of that project.     

Possibility,chance and necessity

Those who deny the usefulness of the concept of “motive” for psychology commonly bring two arguments in support of theirview. The first is that the whole notion of “motive” is “animistic” and “folklorish”, since a motive cannot be directly observed. The second is that “motives” cannot be accurately observed, and therefore are beyond the scope of scientific study, because (a) they are “the secret of the agent”, and (b) the agenthimself has no indubitable knowledge of his “motives”.

In a recent article, Professor MacIver defends the view that the imputation of “motives” is necessary to a complete explanation of behaviour. To the first of the above criticisms, he replies that such a view neglects a part of reality and that since “motives” exist they should be studied by psychology. This reply does nothing to demonstrate the necessity of imputing motives in order to obtain a complete explanation of behaviour. To the second criticism he replies (a) “motives” are not the secret of the agent, and (b) we can only assert that the agent has mistaken his “motive” if we can gain indepen-dent knowledge of it. We can do this, Professor MacIver asserts, by observing typical behaviour in typical circum-stances, and making inferences from the coherence of total situations.

Professor MacIver's replies to the second of the above criticisms are valid only if “motive” is defined as equivalent to “need”, so that we can say “under such-and-such conditions, such-and-such behaviour occurs”. A statement of this type says nothing about the agent's awareness of his goal. When the term “consciousness” is carefully defined along the lines suggested by Boring, the methods of imputation described by Professor MacIver can be seen to lead us only to the agent's “drives”, or “needs”, defined without reference to the agent's awareness of his goal. Professor MacIver uses “motives” to mean “awareness of the goal”, but gives us no clue as to how they may be imputed, and adduces no proof that their imputation is necessary.

A possible criterion of the presence of a “motive” is the degree of direction observable in the organism's varied reac-tions in response to frustration, though the more precise definition of such a criterion must await further experiment.

In view of the ambiguity of the term “motive” and its penumbra of false suggestion, it is desirable that the term be dropped from psychology.