Is this a fallacy, and if so, which?

Question

P1: My opinions change as a result of brain function

P2: Brain function is caused by opinions stored within it (slightly dodgy premise but if you wouldn't mind assuming it to be true, whether it is true or false has no bearing to my question rather this is just an example)

C1: Changing of my opinions is caused by brain function which is caused by my opinions

In this example, the fallacious implication is that changing of opinions is a circular process. However, this is clearly not true and is a logical jump, as we are only talking about specific opinions and specific brain processes, however we are INCLUDING all of them in the idea of this being circular. We are not attributing any properties of a set to the set itself, and for that reason I do not think this can be included in the Fallacy of Composition. What is, then, the term for this fallacy?

Answer 1

I do not believe the argument presents itself as a clear cut informal fallacy. Rather, I believe you have an objectionable premise: circularity is intolerable in language and reason. This is not how informal fallacies are defined according to Damer in his Attacking Faulty Reasoning.

The argument as presented, the interplay between the mental (opinions) and brain state (neurons) is related to the classical dispute over mental causation. If we take a close look at a simple characterization of it, it might help us refine the question. From WP:

The basic problem of mental causation is an intuitive one: on the face of it, it seems that mental events cause physical events (and vice versa), but how can mental events have any causal effect on physical events?

If I think about something, and then change my brain, and then my brain has intuitions that cause me to think differently about something else, why shouldn't I think of opinion formation as a circular process? It seems that the burden is on you to show how the argument fails. Of course, this is part of the broader literature on mental causation, and you adduce no thorough arguments or citations for or against. You do claim:

the fallacious implication is that changing of opinions is a circular process. However, this is clearly not true and is a logical jump, as we are only talking about specific opinions and specific brain processes, however we are INCLUDING all of them in the idea of this being circular.

But circularity is an unavoidable aspect of the reasoning process according to many thinkers. Consider that no definition in the dictionary relies on anything other than words. Thus, in an extended sense, all definitions, per se, are circular. Tautologies and impredicativity seem to be woven inseparably into language. All arguments carry with them presuppositions (SEP). In fact, we seem to be stuck in Neurath's boat. From WP:

We are like sailors who on the open sea must reconstruct their ship but are never able to start afresh from the bottom. Where a beam is taken away a new one must at once be put there, and for this the rest of the ship is used as support. In this way, by using the old beams and driftwood the ship can be shaped entirely anew, but only by gradual reconstruction. - Otto Neurath

Thus, you seem to have taken a position in regards to the Agrippan Trilemma without a clear cut justification of why foundationalism is superior to anti-foundationalism. Since this question about the legitimacy of circularity is an old and complex topic, presuming that the argument as presented is necessarily fallacious would seem to presume that anti-foundationalist beliefs are somehow the only legitimate first-principles in epistemology, which is clearly not a factual statement.

Answer 2

Not sure where the fallacy is. The idea that two processes are mutually dependent or co-occurring is not inherently contradictory or fallacious.

For example, any system of coupled differential equations has similar dynamics.
A simple example is predator-prey models - increase in prey causes increase in predators which causes decrease in prey which causes decreases in predators and so on.

Logically, we if we let B = Brain function, O = Opinions and C(x) = change in x then we have:

P1: C(B) ⇒ C(O)
P2: C(O) ⇒ C(B)
∴
C1: C(O) ⇔ C(B)

Nothing weird about the above.

Answer 3

You wrote down two premises (of which one is more than dodgy), and clearly if both premises are true then changing opinions is a circular process.

When you look for a fallacy, there are two problems:

Changing your opinions could create a feedback loop where the next change is smaller. So I form the opinion that some piece of music is beautiful. Then I change my opinion that it is nice but not that beautiful. Then I change my opinion that it is quite nice, and every time the change is less. That sounds realistic to me and not false.

And of course I can draw a false conclusion from premises without any fallacy if one or more of the premises are not true, which seems to be the case here.