That things come in kinds seems a natural assumption of the human mind: For the human mind, everything is of some kind. Aristotle already made it, quite explicitly, though he spoke of 'categories'.

It is difficult to be precise about such a fundamental concept, but it makes sense to insist that such classes as are considered kinds are characterized by known properties and indeed also satisfy the following:

Kind(Y) --> (EX)(x)(xeX --> xeY) & (EZ)(x)(xeY --> xeZ)

In other words: One must have some idea of the antecedents and consequents of a kind, or again in Aristotelian terms: Of species and genera of a category.