When we speak of possibility, we speak in two ways. We sometimes speak, especially if we are philosophers, of whether it is possible that a certain situation obtain, such as whether it is possible that there be talking donkeys, or that there be beings physically like ourselves who lack consciousness. But we also sometimes speak of whether a certain outcome is possible for a certain agent, such as whether it is possible for a golfer to make a putt, or for an omnipotent being to change the laws of nature. We ought not lay much weight on this linguistic fact, which may be merely an accident of language. But it does offer a concise way of stating the thesis of this essay. The thesis is that possibility for is irreducible to possibility that. Facts about what agents can do cannot be fully reduced to other modal notions. An adequate account of possibility requires appeal to a species of possibility that is fundamentally agentive.