# What fallacy is this?

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?

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.

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.

• But the issue is that brain function and opinions are sets. The entirety of one's opinions does not caused one's brain function and one's entire brain function does not cause the change of a single opinion.
– sket
Commented Nov 23, 2023 at 23:58
• @sket I don’t think set is an appropriate structure to represent your argument Commented Nov 24, 2023 at 0:01
• @sket the problem is that there is a dynamic element not being captured by static sets - you need to index your sets by time, almost like a Filtration in probability theory Commented Nov 25, 2023 at 17:19

It is the false premise fallacy. Your conclusion of a circular argument is based on your "slightly dodgy premise" that you want the readers to ignore:

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)

There are a number of false premises:

1. The map to Brain function is one-to-one

There are a number of processes that set Brain function to true including reading, writing, and comparing opinions. The state of Brain function (True or False) cannot be used to determine the process used to set the current state. Opinion change and opinion storage are two different processes. Equating the two is a source of your circular argument.

1. Brain process function is static.

Brain process is zero until a brain process occurs. An opinion-based process sets the brain process function to true. Once an opinion is changed, the Brain process function is set to false. This dynamic feature prevents a circular argument.