In this article the author seeks to ascertain the answer of the Stoics to the query, what precisely constituted the immutable ground of change. The Stoic conception of identity was rival towards of Academics, epicureans and peripatetics. Unfortunately, however, the very same expression úsia occurs in each with a different sense – consequently the en bloc translation as substance, common since Boethius, is not appropriete. The Stoic conceive of úsia as the substratum, or the stuff of separate individual things, as a rule not remaining the same in changes, though the identity of the thing – its individualizing determination, or – idios poión stays the same. Whence the Stoics, in distindtion of the Academics, account for the growth and decay as change of substratum and not as change of identity – not as rise and extinction. The author further analyses the stoic theory of mixing up and that total blending concerns substratum and pneuma only, which coextensively permeat each other, but not bodies, because these can not interpretate (contrary Todd). With their original conception of “total blending” the Stoa anticipated the modern notion of a ´functional whole´ and distinguished the relation of being a functional part from that of being a spatial part, resp. of being a part of a material whole. The material and pneuma of a separate individual thing permeat each other entirely – they are functional parts of a whol, the identity of which is secured by pneuma, i.e. specific level of integration, or rather the disposition thereto(for). E.g. body and soul of a man are his functional parts, while the body (the parts thereof) can change without loss of his identity – i.e. without change of his soul. With his well documented distinction of these relations of part and the whole the author explains the ontologically gounded stoic principle of non-identity, kindred to the princile of identity indiscernibles proposed by Leibnitz, and reconstructs Stoics´noetic principle of difference. Upon the basis of these principles he consistently interprets apparently contradictory fragmenta, argues the inadequacy of Sedley´s commonly accepted exposition of the Stoic principle of identity and criticises Lewis unfinished opposition towards Sedley. Embarking from these beginnings the author reconstructs and elucidates the paradox of Dion and Theon (i.e. argument about two individuals inhabiting one body), the argument of Mnesarchus concerning comming into being and vanishing into oblivion of separate individual things and the original Stoic explanation of the identity of Theseus´ ship.