omission / comission

This is a distinction that some moral philosophers are fond of. This is my take on it: when we are evaluating the actions of others (or our past selves), there is a difference between considering (or having it in one's "horizon of possibilies") an option, and not doing it, and not even considering it (and not doing it). This does not mean that one is excusable, or whatever, and one not; it just means that we should react to the two very differently; fixing each error calls for a different prescription, etc. On the other hand, in my own decision making, about what to do next, this distinction can play no possible role. After all, if I am at the point where I wonder "would this be an error of omisssion or comission," then I am already at the point of considering it, and would perforce be an error of comission.

The upshot of this is that, in cases such as the famous trolley problem, the omission / comission distinction has no bearing. It is a moral failing to hold that it does. I say this because I feel it is a way of avoiding responsibility. Taking responsibility for one's surroundings involves knowing what will happen depending on what you do next, and taking the actions appropriate to your aims.