In an article from 2019 entitled "Imagination and Objectivity in Fichte’s Early Wissenschaftslehre", Johannes Haag says that the Theoretical Part of Fichte's 1794 Foundation of the Entire Science of Knowledge (Grundlage der gesamten Wissenschaftslehre) sets for itself the following task: "to think of the I and the non-I as causally interacting substances". In what follows I want to explain why this description of Fichte's project of theoretical philosophy is misleading and offer a corrective.

There is one factually incorrect part to Haag's description, which is that, according to Fichte, only the "I", the "Self", is a substance. Fichte defines substance as the "totality of all that is" ("allumfassendes"), the "ambit of all realities" ("Umkreis aller Realitäten"). Because only the "I", and not the "non-I", has the ability to "posit" what is, the non-I cannot be a substance. Only the "I" is a substance.

This minor correction aside, the larger problem with Haag's account, and indeed, with most intepretations of Fichte 1794 Foundation, is a failure to clarify the meaning of Fichte's philosophical terms. What does it mean to say that the "I" and the "non-I" are causally interacting substances? Haag doesn't eluciate his formulation, but I want to show that it is truly in need of elucidation.

One possible, though certainly incorrect, reading of the claim that the "I and the non-I" are "causally interacting substances" is to understand causality and substance in a common physical sense. The "I" exists in the physical world as one substance. The rest of the world, the "non-I" is everything else, another substance, and they interact causaly with one another. The non-I bombards the I with stimuli which produces its thoughts or intuitions, while the I acts on the world, changing it according to its needs and wants, etc. This cannot be what Fichte means, since to say that the "I" is a physical substance that is causaly acted upon by the world would be "Spinozism" or "dogmatic realism", a position Fichte explicitly rejects. Dogmatic realism sees the "I" as part of the causal nexus of the empirical world, and Fichte's philosophy is meant to counter this view.

Another possibility is to say that the kind of causality at hand is not normal, physical, efficient causality, but a 'transcendental' causality. In the theoretical realm, this would be something like Kant's notion of the "affectation" of a "Thing-in-itself". However, this descends into nonsense. As Jacobi famously pointed out in David Hume über den Glauben, how else is one to understand causality, or affection, if not in its normal, physical sense, where one physical object impinges on another?

Luckily, Fichte offers us alternative definitions of causality and substance, and it is these defintions, that, I argue, are the correct way to read him. These definitions define causality and substance in terms of propositional logic, in terms of a logic that makes truth-claims about the empirical world.

The logical construal of causality

Both "causality" and "substance" are versions of "interdetermination" (Wechselbestimmung). Fichte defines interdetermination like so:

By means of the determination of reality or negation of the Self, we determine at the same time negation or realtiy of the Not-Self; and visa-versa.

Durch die Bestimmung der Realität oder Negation des Ich wird zugleich die Negation oder Realität des Nicht–Ich bestimmt; und umgekehrt.

This is a version of the law of the excluded middle. We can see this by replacing the "Self" and "Not-Self" with the propositions p and ¬p. The "reality", or truth, of p, determines the "negation", or falsity, of ¬p. We get from a simple proposition p to the topic of the "Self" and "Not-Self" by observating that "interdetermination" is, for Fichte, about "degrees of reality":

Divide, for example, the totality of reality into 10 equal pieces; posit 5 of them in the Self, then 5 pieces of negation are necessarily posited in the Self

Theilet z.B. die Totalität der Realität in 10 gleiche Theile; setzt deren 5 in das Ich; so sind nothwendig 5 Theile der Negation in das Ich gesetzt

The "Self" is a rational agent who judges, which among other things, means that the Self makes claims about what is, empirically, the case. Thus, empirical reality can be construed as the set of propositions that the Self makes about the empirical world. A certain number of these propositions will be false, since it is inherent in the notion of a rational agent that our judgments about what is the case can err. Thus for any set of n propositions that the self makes S = (p₁, p₂, p₃,...) there is corresponding set of the contradictory propositions S' = (¬p₁, ¬p₂, ¬p₃,...). Precisely those propositions will be true in set S that will be false in the contradictory set S', and, visa versa, precisely those prositions will be false in set S that are true in set S'. This is just the law of the excluded middle applied to a set of propositions.

According to this logical construal of Fichte's notion of "interdetermination," the "Not-Self" is simply the negation of everything the Self takes to be the case.

Fichte now defines causality according to the observation that this relationsip between the Self the Not-Self is asymetric. Only the Self can judge, only the Self can put forward propositions. The only thing the Not-Self can do is prove those propositions wrong. Thus the Not-Self is the principle of correction. The Not-Self is that which corrects the Self's incorrect empirical judgments. The Not-Self is objectivity. It is the corrective to the Self's ability to make incorrect claims about what is the case.

In Fichte's terms, the concept of causality says:

Das Nicht-Ich hat, als solches, an sich keine Realität; aber es hat Realität, insofern das Ich leidet.

To be continued...