There are two sources of our modal intuitions which have to be explained - physical (natural) modality and metaphysical modality. The problem of explanation is presented as a dispute between modal realism and modal anti-realism. Traditional explanations of modalities are classified according to the strength of their anti-realism. They are unsuccessful because they are not able to show how to extract modal properties out of something which is ultimately non-modal. Even the thesis of supervenience - modal properties supervene on non-modal, is explanatory inadequate. Supervenient (modal) properties must necessary covary with their subvenient (non-modal) properties. The modal force of this necessity is irreducible. I argue for modal realism, although I recognize epistemological difficulties of this position.