If my beliefs, by so existing, change the outcome of reality
So, if your writing "here be dragons" on a map results in someone encountering a dragon when traveling to the mapped area (a very popular theme in SF/F), how useful is the concept of reality?
You don't need to reject realism to reject the idea that beliefs can only be reflections of reality, rather than a causal part of it.
You don't need to, no. But the concept of reality is less useful if all you mean by it is future inputs to test the accuracy of your beliefs, as opposed to a largely unchanged territory that you map. If you have to build the proverbial epicycles to keep your belief alive, you might want to consider a simpler model.
The map is part of the territory.
Is this a useful assertion? If so, how?
How accurately does your map represent your map?
Not sure what you mean by this. That beliefs can be nested? Sure. That the term "map" presumes some territory it maps? It sure does, in the realist picture. Hence my preference for the term "model" or even "belief". Of course, a realist can ask something like "but what is your model a model of [in reality]?", which to me is not a useful question if your reality is changing depending on the models.
At the risk of dogpiling:
So, if it is true in reality that your writing "here be dragons" on a map results in someone encountering a dragon when traveling to the mapped area...
The Litany of Tarski (formulated by Eliezer, not Tarski) reads
If the box contains a diamond,
I desire to believe that the box contains a diamond;
If the box does not contain a diamond,
I desire to believe that the box does not contain a diamond;
Let me not become attached to beliefs I may not want.
This works for a physical realist, but I have been feeling uncomfortable with it for some time now. So I have decided to reformulate it in a more instrumental way, replacing existential statements with testable predictions. I had to find a new name for it, so I call it the Litany of Instrumentarski:
If believing that there is a diamond in the box lets me find the diamond in the box,
I desire to believe that there is a diamond in the box;
If believing that there is a diamond in the box leaves me with an empty box,
I desire to believe that there is no diamond in the box;
Let me not become attached to inaccurate beliefs.
Posting it here in a hope that someone else also finds it more palatable and unassuming than straight-up realism.
EDIT: It seems to me that this modification also guides you to straight-up one-box on Newcomb, where the original one is mired in the EDT vs CDT issues.
EDIT2: Looks like the above version resulting in people confusing desiring accurate beliefs with desiring diamonds. It's about accurate accounting, not about utility of a certain form of crystallized carbon.
Maybe the first line should be modified to something like "If I later find a diamond in the box...", or something. How about the following?
If I will find a diamond in the box,
I desire to believe that I will find a diamond in the box;
If I will find no diamond in the box,
I desire to believe that I will find no diamond in the box;
Let me not become attached to inaccurate beliefs.
For some reason the editor does not let me use the <strike> tag to cross out the previous version, not sure how to work around it.