Without delving into details of discrepancies which
may exist between the “Perpetual Peace” essay and Kant’s more
difficult and fuller discussion in The Metaphysical Elements of
Justice, for my purposes the most important question is this:
does Kant mean to derive or deduce cosmopolitan right from
the fact of the sphericality of the earth’s surface? What is the
status of this fact in Kant’s moral argument? If indeed we were
to assume that Kant used the sphericality of the earth as a justificatory
premise, wouldn’t we then have to conclude that he
had committed the naturalistic fallacy? Just because all castles
everywhere are built on sand, it still does not follow that mine
should be so built as well. Likewise, just because I must, somewhere
and at some point, come into contact with other human
beings and cannot flee them forever, this does not imply that
upon such contact I must treat them with the respect and dignity
to be accorded every human being