Borders enclose and separate us. We assign to them tremendous significance. Along them we draw supposedly uncrossable boundaries within which we believe our individual identities begin and end, erecting the metaphysical dividing walls that enclose each one of us into numerically identical, numerically distinct, entities: persons. Do the borders between us - physical, psychological, neurological, causal, spatial, temporal, etc. - merit the metaphysical significance ordinarily accorded them? The central thesis of I Am You is that our borders do not signify boundaries between...