In a passage quoted here, Jerry Coyne objected to the “moral” in “moral responsibility”:

To me, that means that the concept of “moral responsibility” is meaningless, for that implies an ability to choose freely. Nevertheless, we should still retain the concept of responsibility, meaning “an identifiable person did this or that good or bad action”. And, of course, we can sanction or praise people who were responsible in this sense, for such blame and praise can not only reinforce good behavior but is salubrious for society.

Suppose someone completely insane happens to kill another person, under the mistaken belief that they are doing something completely different. In such a case, “an identifiable person did this or that good or bad action,” and yet we do not say they are responsible, much less blame such a person; rather we may subject them to physical restraints, but we no more blame them than we blame the weather for the deaths that it occasionally inflicts on people. In other words, Coyne’s definition does not even work for “responsibility,” let alone moral responsibility.

Moral action has a specific meaning: something that is done, and not merely an action in itself, but in comparison with the good proposed by human reason. Consequently we have moral action only when we have something voluntarily done by a human being for a reason, or (if without a reason) with the voluntary omission of the consideration of reasons. In exactly the same situations we have moral responsibility: namely, someone voluntarily did something good, or someone voluntarily did something bad.

Praise and blame are added precisely because people are acting for reasons, and given that people tend to like praise and dislike blame, these elements, if rightly applied, will make good things better, and thus more likely to be pursued, and bad things worse, and thus more likely to be avoided. As an aside, this also suggests occasions when it is a bad idea to blame someone for something bad; namely, when blame is not likely to reduce the bad activity, or by very little, since in this case you are simply making things worse, period.

Stop, Coyne and others will say. Even if we agree with the point about praise and blame, we do not agree about moral responsibility, unless determinism is false. And nothing in the above paragraphs even refers to determinism or its opposite, and thus the above cannot be a full account of moral responsibility.

The above is, in fact, a basically complete account of moral responsibility. Although determinism is false, as was said in the linked post, its falsity has nothing to do with the matter one way or another.

The confusion about this results from a confusion between an action as a being in itself, and an action as moral, namely as considered by reason. This distinction was discussed here while considering what it means to say that some kinds of actions are always wrong. It is quite true that considered as a moral action, it would be wrong to blame someone if they did not have any other option. But that situation would be a situation where no reasonable person would act otherwise. And you do not blame someone for doing something that all reasonable people would do. You blame them in a situation where reasonable people would do otherwise: there are reasons for doing something different, but they did not act on those reasons.

But it is not the case that blame or moral responsibility depends on whether or not there is a physically possible alternative, because to consider physical alternatives is simply to speak of the action as a being in itself, and not as a moral act at all.