So long as οὐσία and ὑπόστασις had been convertible terms, the one Latin word _substantia_, the etymological equivalent of ὑπόστασις, had sufficed for both. When the two words became differentiated in Greek, it became advisable to mark the difference. However, the word _essentia_, the natural equivalent for οὐσία, jarred upon a Latin ear.[583] Consequently _substantia_ was claimed for οὐσία, while for ὑπόστασις a fresh equivalent had to be sought. This was found in _persona_, whose antecedents may be those of “a character in a play,” or of “person” in the juristic sense, a possible party to a contract, in which case Tertullian may have originated this usage.[584] Such Western practice would tend to stimulate the employment of the corresponding Greek term πρόσωπον, whose use hitherto seems to have been subordinate to that of ὑπόστασις.[585] And, finally, the philosophic terms φύσις and _natura_ came into use. In the second century φύσις had been distinct from οὐσία and identical with Reason.[586] But in the fourth century it came to be identified with οὐσία,[587] and afterwards again distinguished from it, whereas the Monophysites identified it with ὑπόστασις. To sum up, then. We have in Greek four terms, οὐσία, ὑπόστασις, πρόσωπον, φύσις, and in Latin three, _substantia_, _persona_, _natura_, the two series not being actually parallel even to the extent to which they are so in appearance. Times have changed since Tertullian’s[588] loose and vague usage caused no remark; when Jerome, thinking as a Latin, hesitates to speak of τρεῖς ὑποστάσεις, by which he understood _tres substantias_, and complains that he is looked upon as a heretic in the East in consequence. There is a remarkable saying of Athanasius which is capable of a wider application than he gave it: it runs as follows:[589] “They seemed to be ignorant of the fact that when we deal with words that require some training to understand them, different people may take them in senses not only differing but absolutely opposed to each other.”[590] Thus there was an indisposition to accept οὐσία. The phrase was not understanded of the people.[591] A reaction took place against the multiplicity of terms; but the simple and unstudied language of the childhood of Christianity, with its awe-struck sense of the ineffable nature of God, was but a fading memory, and on the other hand the tendency to trust in and insist upon the results of speculation was strong. Once indeed the Catholic doctrine was formulated, then, though not till then, the majority began to deprecate investigations as to the nature of God.