From the logic point of view, counterfactuals are unproblematic, in that I can prove consistency of my favorite counterfactual logic by exhibiting a model. Then as far as a logician is concerned, we are done: our counterfactual worlds live in the mathematical structure of the exhibited model.
From the computer science point of view a little more is required, but as luck would have it, we can implement counterfactuals in some causal models. If your causal model is an actual circuit, then not only is it perfectly meaningful to ask “the output of the circuit is 1, what would be the output if I changed gate_0212 from OR to AND?” but it is possible to implement the counterfactual directly, and check. This is because we know enough about the causal model to ensure counterfactual invariance (e.g. other gates do not change). People use this kind of counterfactual reasoning to debug programs and circuits all the time! So from the “comp. sci” point of view, counterfactuals are unproblematic. The counterfactual universe “exists” in the operational sense of us having an effective procedure to get us there.
The problem arises when you are trying to deal with relatively poorly defined problems, like say problems in statistics or machine learning involving measurements of human populations or vitals in a patient with a ton of uncertainty about functional mechanisms and their invariance. Actually even in that case, people try to construct effective procedures to reach counterfactual universes, or something close (see, e.g. Imai’s paper: http://imai.princeton.edu/research/Design.html). The question is then the following. Do counterfactual worlds in this case:
(a) not exist (ontological problem).
(b) exist, but we do not have a one to one mapping from the information we have to a unique counterfactual world describing the question we are interested in, even in principle (identification problem).
(c) exist, we do not have a one to one mapping from the information we have to a unique counterfactual world describing the question we are interested in, but we can get such a mapping if we learn a LOT more about the problem, and observe many many more variables (ignorance problem).
From the logic point of view, counterfactuals are unproblematic, in that I can prove consistency of my favorite counterfactual logic by exhibiting a model. Then as far as a logician is concerned, we are done: our counterfactual worlds live in the mathematical structure of the exhibited model.
From the computer science point of view a little more is required, but as luck would have it, we can implement counterfactuals in some causal models. If your causal model is an actual circuit, then not only is it perfectly meaningful to ask “the output of the circuit is 1, what would be the output if I changed gate_0212 from OR to AND?” but it is possible to implement the counterfactual directly, and check. This is because we know enough about the causal model to ensure counterfactual invariance (e.g. other gates do not change). People use this kind of counterfactual reasoning to debug programs and circuits all the time! So from the “comp. sci” point of view, counterfactuals are unproblematic. The counterfactual universe “exists” in the operational sense of us having an effective procedure to get us there.
The problem arises when you are trying to deal with relatively poorly defined problems, like say problems in statistics or machine learning involving measurements of human populations or vitals in a patient with a ton of uncertainty about functional mechanisms and their invariance. Actually even in that case, people try to construct effective procedures to reach counterfactual universes, or something close (see, e.g. Imai’s paper: http://imai.princeton.edu/research/Design.html). The question is then the following. Do counterfactual worlds in this case:
(a) not exist (ontological problem).
(b) exist, but we do not have a one to one mapping from the information we have to a unique counterfactual world describing the question we are interested in, even in principle (identification problem).
(c) exist, we do not have a one to one mapping from the information we have to a unique counterfactual world describing the question we are interested in, but we can get such a mapping if we learn a LOT more about the problem, and observe many many more variables (ignorance problem).