CHAPTER ONE

The Life of p

1. Principles of Noncontradiction

1.1.

To be a philosopher, according to Aristotle, is to be an authority on this principle:
(OPNC) For the same thing to hold good and not to hold good simultaneously of the same thing and in the same respect is impossible (given any further specification which might be added against the dialectical difficulties). (Gamma 3, 1005b18ā€“21)1
The authority comes from the extraordinary generality of philosophical understanding:
It is appropriate for him who has the best understanding about each genus to be able to state the firmest principles of that actual subject, and hence, when his subject is being qua being, to state the firmest principles of everything: and this man is the philosopher. (Gamma 3, 1005b8ā€“12)
(Strictly speaking, there is only an analogy between a philosopher and a scientist; Aristotle says elsewhere that philosophy is not directed at any genus whatsoever.)
The remark about the philosopher should be read in the context of the second aporia of Metaphysics Beta, which Aristotle revisits in the opening of Gamma 3:
We have to say whether it falls to one, or a different, science to deal with the things that in mathematics are termed axioms, and with substance.2 (Gamma 3, 1005a19ā€“21)
In Beta he called an axiom a ā€œprinciple of reasoning.ā€ Such principles are
the common opinions from which all people draw proofsā€”for example, that it is necessary either to affirm or to deny everything, and that it is impossible to be and not to be at the same time, and any other such propositions. (Beta 2, 996b26ā€“30)
The aporia is finally resolved in Gamma, with its new characterization of first philosophy as the science of being qua being.3 For now the principles of reasoning can be described as ā€œholding of being qua being,ā€ and so:
It is indeed obvious that the investigation of these [the axioms] too falls to one science, and that the philosopherā€™s; for they hold good of being qua being and not of a certain genus, separate and distinct from others. (Gamma 3, 1005a21ā€“24)
Because the axioms hold of being qua being, they are in play wherever truth is at stakeā€”for example in the special sciences. But because of their peculiar generality they cannot be comprehended by studying a specific kind of beings. They cannot be incorporated within the subject matter of a special science.
Aristotle notes that while scientists such as geometers and arithmeticians must use these principles, they do not actually investigate them. The exceptions are certain students of nature, who mistakenly think that they can comprehend the principles as part of their field:
But that is not surprising, since they alone have considered that they were investigating the whole of nature, i.e., that which is. But since there is someone still further above the student of nature (for nature is one particular genus of what there is), the investigation of these things must fall to him who studies what is universal and primary substance. The study of nature is also a wisdom but not primary. (Gamma 3, 100a32ā€“35)
Their mistake is to identify nature with the whole of being. Nature is a whole, Aristotle saysā€”but a limited one, since ā€œthere is someone still further above the student of natureā€: the philosopher. It is the philosopher who studies ā€œwhat is universal and primary substance.ā€
But what does this have to do with the other pointā€”that it is the philosopher and not the natural scientist who studies the principles of reasoning?
The answer begins with a recognition that the object of natural scienceā€”the whole of natureā€”does not contain thinkers or thinking. The study of the intellect goes beyond physics. But that is only a beginning. We must explain this ā€œbeyond,ā€ and why the study of thinkers and thinking is more inclusive than the study of nature.
My suggestion will be that principles of reasoning apply to intellects as principles of thinking, but to natural substances and their predicative determinations as principles of being. In particular, nature can be identified with everything to which the law of noncontradiction applies merely as a principle of being, and so with all the predicative facts (both positive and negative.) It will turn out that the larger whole which includes thinking is not richer in predicative content than nature. In other words, nature includes every determinable and every determination. A study that goes beyond nature goes beyond these too.4
Natural scientists do not study the principles of reasoning as such. They do not reflect on them as principles of thinking, or on the unity of thinking and being.5

1.2.

Aristotle says that OPNC is the firmest principle because
(PPNC) It is impossible for anyone to believe that the same thing is and is not. (Gamma 3, 1005b22ā€“25)
If OPNC is the ontological principle of noncontradiction, PPNC is the psychological principle of noncontradiction.6 The ontological principle is a principle of being. It appears to place a limit on what can be. The psychological principle is a principle of thinking. It appears to place a limit on what can be believed or thought.7
Under the influence of fin de siĆØcle anti-psychologism, commentators have become highly sensitive to possible confusions of OPNC and PPNC. But Aristotle often seems uninterested in the difference between them. Indeed, he calls OPNC a principle of reasoning.

1.3.

In Gamma 3, Aristotle derives PPNC directly from OPNC.
This is usually explained as follows. Suppose a believer is a sort of substance. And suppose a particular belief is a property of this substance. Having the belief that p is correlated with having the property expressed by the predicate Belief (ā€¦, p); not having this belief is correlated with the property expressed by the predicate not-Belief (ā€¦, p).8 By OPNC, these predicates cannot be co-instantiated. PPNC follows.
I am going to argue that all this is wrongā€”both in itself and as a reading of Aristotle. A believer is not a natural substance; a belief is not a property; nor are beliefs joined together in a believer as properties are joined together in a substance.9 PPNC is not an instance of OPNC.

2. The Psycho-logical Problem

2.1.

It is often said that logical principles govern thinking. But what sort of government is this? And what is the source of its authority?
The philosophical concern that I try to convey by these questions can be described as the psycho-logical problem. We can distinguish four approaches to this problem corresponding to four views on the provenance of logical principles:
(1) Psycho-logicism:
ā†
(2) Logo-psychism:
ā†’
(3) Psycho / logical dualism:
ā‰ 
(4) Psycho / logical monism.10
These four approaches can be distinguished by their respective treatment of the difference between PPNC and OPNC.
Psycho-logicism takes PPNC to be a law of our psychology, and OPNC as a report on how things look to us given PPNC. Logo-psychism takes PPNC to be an application of OPNC to human psychology. Whether the principle of noncontradiction is properly a principle of thinking or of being is a matter of serious disagreement between these different approaches. Nonetheless, they both agree on this: that there is in the end only one such principle.
Psycho / logical dualism takes PPNC and OPNC to be logically independent generalizations and denies that PPNC is a logical principle. To these, the dualist adds a third principle of noncontradiction, which is not a generalization but a normative requirement: that one should not contradict oneself.
Psycho / logical monism takes a belief or judgment to be a unity that is immanent and thus only identifiable within a larger unityā€”that of consciousness and language. Since a unity in consciousness is the same as a consciousness of unity, the monist holds that a belief or a judgment is as such self-conscious, and we shall come to see that such self-consciousness is essentially contained in the use of language. That is, we shall come to see that this self-consciousness is essentially the expression of consciousness by language. From the monist point of view, a simple propositional sign displays a possible act of consciousness, but the identity of this act depends on the uses of a proposition within other propositional contexts. Hence, for example, understanding p as an expression of consciousness depends on understanding the use of p in negation. As such, from this point of view we come to see that no conscious act is displayed or specified by the proposition of the form (p and ~p) and therefore no judgment or assertion is displayed by ~(p and ~p). This means that ~(p and ~p) and (p and ~p) are not genuine propositions. Understanding OPNC consists in seeing that the repetition of p in these logical contexts is self-cancelling. The difference between OPNC and PPNC will then correspond to the difference between the consciousness expressed by ā€œpā€ and the self-consciousness expressed by ā€œI think p.ā€ But this talk of ā€œdifferenceā€ does not mean that PPNC and OPNC are two different principles. In the end the monist will say neither that they are two, nor one. Or rather: that they are the same and different.
This is what I myself want to say.

2.2.

Frege singles out psycho-logicism11 as the main obstacle to understanding the idea of thinking as governed by logic. He seems to have in mind a kind of logical naturalismā€”similar to the view that Aristotle criticizes in Gamma 3, which assigns the study of principles of reasoning to natural science.12 If that were right, ...