... it has been suggested that e originally went with the highest pitch accent, while o appeared in syllables of a lower pitch. But if there is any foundation for the theory, which is by no means certain, its effects have been distorted and modified by all manner of analogical processes. Thus poimen with acute accent and daimon with the acute accent on the preceding syllable would correspond to the rule, so would aletes and epos, but there are many exceptions like odos where the ... — Project Gutenberg Encyclopedia