His first act was to repudiate the Henoticon, a deed of union, originating, it is supposed, with Acacius, patriarch of Constantinople, and published by the emperor Zeno with the view of allaying the strife between the Monophysites and their opponents in the Eastern church.
If the recognition of physics and logic as two studies coordinate with ethics is sufficient to differentiate the mature Zeno from the Cynic author of the Republic, no less than from his own heterodox disciple Aristo, the Cleanthes.
The short reign of Basiliscus (474-476) favoured the Monophysites, but the restoration of the rightful emperor Zeno marked an attempt at conciliation.
Antigonus Gonatas, bluff soldier-spirit that he was, heard the Stoic philosophers gladly, and, though he failed to induce Zeno to come to Macedonia, persuaded Zeno's disciple, Persaeus of Citium, to enter his service.
First, he made a number of leathern tubes the ends of which he contrived to fix among the joists and flooring of a fine upper-room in which Zeno entertained his friends, and then subjected it to a miniature earthquake by sending steam through the tubes.
In all probability Zeno did not observe that in his controversial defence of Eleaticism he was interpreting Parmenides's teaching anew.
That is to say, not perceiving that the same thing may be at once like and unlike in different relations, Zeno regarded the attribution to the same thing of likeness and unlikeness as a violation of what was afterwards known as the principle of contradiction; and, finding that plurality entailed these attributions, he inferred its unreality.
The emperors Zeno and Anastasius had been strongly suspected of it, and the Roman bishops had refused to communicate with the patriarchs of Constantinople since 484, when they had condemned Acacius for accepting the formula of conciliation issued by Zeno.
At the same time the antiquarian study of Stoic writings went on apace, especially those of the earliest teachers - Zeno and Aristo and Cleanthes.
Accordingly Aristo, holding to Cynicism when Zeno himself had got beyond it, rejected two of these parts of philosophy as useless and out of reach - a divergence which excluded him from the school, but strictly consistent with his view that ethics alone is scientific knowledge.