  This objection assumes a purely psychological criterion of identity,  however, one in which, further, “person” is what's known as a substance concept, a term designating a kind to which an  individual always and essentially belongs throughout its existence.  But as we saw earlier, “person” might be merely a   phase sortal, designating a kind to which the individual belongs – if it does at all – for only part of its existence.  This could mean, then, that I, now a person, could still be  identical qua individual, to some organism – a fetus,  say – that was not a person. Thus if some past fetus is  identical to me – if we are one and the same animal, or  organism – then he did indeed have a future like ours (Marquis  1998).