None of his works have come down to us. With regard to his philosophical system, in spite of his boast of being self-taught and having borrowed from no one, he clearly derived the chief part of his natural philosophy from Democritus, and of his moral philosophy from Aristippus and the Cyrenaics. He considered human happiness the end of all philosophy, and agreed with the Cyrenaics that pleasure constituted the greatest happiness; still this theory in his hands acquired a far loftier character; for pleasure, in his idea, was not a mere momentary and transitory sensation, but something lasting and imperishable, consisting in pure mental enjoyments, and in the freedom from pain and any other influence which could disturb man's peace of mind. And the _summum bonum_, according to him, consisted in this peace of mind; which was based upon correct wisdom ({ ~GREEK SMALL LETTER PHI~}{ ~GREEK SMALL LETTER RHO~}{ ~GREEK SMALL LETTER OMICRON WITH OXIA~}{ ~GREEK SMALL LETTER NU~}{ ~GREEK SMALL LETTER ETA~}{ ~GREEK SMALL LETTER SIGMA~}{ ~GREEK SMALL LETTER IOTA~}{ ~GREEK SMALL LETTER FINAL SIGMA~}).
In his natural philosophy he embraced the atomic theories of Democritus and Diagoras, carrying them even further than they themselves had done, to such a degree that he drew upon himself the reproach of Atheism. He regarded the Gods themselves as consisting of atoms, and our notions of them as based upon the images ({ ~GREEK SMALL LETTER EPSILON~}{ ~GREEK SMALL LETTER IOTA WITH PSILI AND OXIA~}{ ~GREEK SMALL LETTER DELTA~}{ ~GREEK SMALL LETTER OMEGA~}{ ~GREEK SMALL LETTER LAMDA~}{ ~GREEK SMALL LETTER ALPHA~}) which are reflected from them, and so pass into our minds. And he believed that they exercised no influence whatever on the world, or on the actions or fortunes of man.
_Theodorus_ was a native of Cyrene, who flourished about B.C. 320. He was of the Cyrenaic sect, and the founder of that branch of it which was called after him, the Theodorean; though we scarcely know in what his doctrines differed from those of Aristippus, unless they were, if possible, of a still more lax character. He taught, for instance, that there was nothing really wrong or disgraceful in theft, adultery, or sacrilege; but that they were branded by public opinion to restrain fools. He is also reproved with utter atheism; and Cicero classes him with Diagoras, as a man who utterly denied the existence of any Gods at all.