I am trying to understand how Greek verbs are formed, having just begun learning their formation in present active indicative. The model verb used is λύω, which I understand to be formed as such:
The explanations I have found for the thematic vowel include:
796. The thematic verbs are so named because in a majority of their forms the personal ending (819–821) is preceded by ο⁄ε (ο before μ or ν, or in the optative mode, otherwise ε), which is called the thematic vowel. Thus, λυο⁄ε (λύω) is called the theme, to which the personal endings (819–821) are attached.
―Wright/Pharr: Homeric Greek
Further, in Shelmerdine:
You’ll notice that all the present active verb forms contain some form of an o or e vowel:
This is the thematic vowel, which regularly appears in certain forms as an e, in others as an o. We can describe a thematic verb like λύω as consisting of three parts: stem, thematic vowel, and personal ending.
―Shelmerdine, C. W.: L. A. Wilding’s Greek for Beginners, Focus Publishing / R. Pullins Co., Newburyport, 2001, pp. 6f.
In the following table, she lists the verb forms as λύ-ω, λύ-εις, λύ-ει, λύ-ο-μεν, λύ-ε-τε, λύ-ουσῐ(ν), only using a hyphen to show the thematic vowel for the plurals. None of these explanations therefore leave me with a proper understanding of what is going on. Based off of Wright/Pharr, I would have expected 1st person singular to be -ε-ω and 3rd person plural to be -ε-υσῐ(ν), as their explanation specifies that it is -ε- except before -μ and -ν (which yields an -ο-). Is there a (historical) linguistic explanation for why these two forms apparently do not follow the rules explained by Wright and Pharr? Or am I missing something obvious? (In which case I apologise!)