+1 for coming up with such an interesting argument
I think it's helpful to define terms for something like this. I realize you linked to another post describing them, but just to avoid any confusion:
internal locus of control - believing that my decisions are under my control external locus of control - believing that my decisions are not under my control
"Things under your control" (more generally, free will) is an ill-defined concept: you are an entity within physics; all of your actions and thoughts are fully determined by physical processes in your brain. Here, I will assume that "things under your control" are any things that are controlled by your brain, since it is a consistent definition, and it's what people usually mean when they talk about things under one's control.
Involuntary responses are not under your control and are not "determined by physical processes in your brain", but are considered actions. Voluntary responses are also influenced by factors occurring outside your brain. If you're tired, you are not likely to do any heavy exercise although you are able to choose to do so. If you see an explosion in front of you, you are likely to drop to the ground or run away.
maybe add physical traits, like height or attractiveness to the "internal factors" category
Yes, internal locus of control factors such as clothing, diet, or hair style are a major influence on attractiveness, but height; I have never heard anyone make that argument before. How is height under my control or what sort of arguments could be made in favor of such a belief? I recognize you are not actually arguing this is the case, but I'm not sure how you could even consider this to be a plausible argument.
It's true that one can measure his IQ, and that IQ rarely changes much, but still: if you consider IQ fixed and external factor out of your control, then you must consider your thought processes restricted to some set and therefore, not totally under your control. ... You shouldn't consider any functions of your current brain state as external when discussing locus of control, since such viewpoint is actually counterintuitive and, therefore, makes you prone to errors.
IQ places a limit on your ability to learn new things, true, but you are still able to determine what you choose to learn. I do not have a limitless amount of money, but I am still able to choose what I buy. Are you saying that income must also be considered completely internal, and if not the things I buy must be external? Everything is limited by something. I consider the limit to be external and out of my control, and the choices I make within those limits to be internal. I don't think that the limit and the choice are one and the same or grouped in some fashion that requires them to be kept together.
Involuntary responses are not under your control and are not "determined by physical processes in your brain", but are considered actions. Voluntary responses are also influenced by factors occurring outside your brain. If you're tired, you are not likely to do any heavy exercise although you are able to choose to do so. If you see an explosion in front of you, you are likely to drop to the ground or run away.
I see now (after reading yours and janos' comments), that my definition isn't perfect; but I think if you exclude some brain parts and i...
This is a sort-of response to this post.
"Things under your control" (more generally, free will) is an ill-defined concept: you are an entity within physics; all of your actions and thoughts are fully determined by physical processes in your brain. Here, I will assume that "things under your control" are any things that are controlled by your brain, since it is a consistent definition, and it's what people usually mean when they talk about things under one's control.
So, you may be interested in the question: how much one's success depends on his thoughts and actions (i.e. things that are controlled by his brain) vs. how it depends on the circumstances/environment (i.e. things that aren't)? Another formulation: how you can change one's life outcomes if you could alter neural signals emitted by his brain?
We also could draw the borderline somewhere else; maybe add physical traits, like height or attractiveness to the "internal factors" category, or maybe assign some brain parts to the "external factors" category. The question whether your life success is mostly determined by "internal factors" or "external factors" would remain valid -- and we call it "internal vs. external locus of control" question.
But what happens when we assign IQ to the "external factors" category?
IQ test is an attempt to measure some value, which is supposed to be a measure of something like quality of one's thinking process. So, this value can be seen as a function IQ(brain), which maps brains to numbers. Your thoughts and actions don't depend on your IQ score; IQ score depends on your thoughts. That's how the causal arrows are arranged.
But it's possible to ask, what can we change if we can change brain, conditional on the fixed IQ score. But then the "free will" intuition collapses; it's hard to imagine what we could change if our thought processes were restricted in some weird way. And such question is hardly practical, in my opinion. It's true that one can measure his IQ, and that IQ rarely changes much, but still: if you consider IQ fixed and external factor out of your control, then you must consider your thought processes restricted to some set and therefore, not totally under your control.
Define "things under your control" as "things under your brain neural signals' control", and then we will have a consistent definition, and we will find ourselves in the common sense domain. Declare that everything is under control of physics, and then we will, again, have a consistent definition of "things under your control" (empty set), and now we are in the physics domain. Both cases are quite intuitive.
But when we consider IQ external, "things under your control" are your thoughts, but not quite; we can control our thoughts, but only as long as they reside on some weird manifold of thought-space. I guess that in such case, your "free will" intuitions would be disrupted. Basically, we can't slice some part of what we call "personality" out and still have our intuitions about personality and free will sane.
TL; DR: You shouldn't consider any functions of your current brain state as external when discussing locus of control, since such viewpoint is actually counterintuitive and, therefore, makes you prone to errors.