Here's what the book has to say, verbatim (full citation at the end of the post):
"Aegeus, like Erechtheus, is another form of the god Poseidon. This is indicated by his connection with the Aegean Sea and by the tradition that Poseidon rather than Aegeus was Theseus' father." (p. 555)which is followed by this endnote:
"And by his link with the cult of Apollo Delphinius, i.e., Apollo as a god of spring, when the sea becomes navigable and the dolphins appear as portents of good sailing weather." (p. 571)
|Aegeus meeting with Themis|
However. It does neatly solve the paternity problem of Theseus, and to argue that Aegeus could NOT have been an aspect of Poseidon imposes human limitations on gods which, for all any of us know, are able to do much, much, more than the occasional shape-shift to seduce a woman. Poseidon in particular, as god of the seas and Earth-Shaker, comes off as pretty mighty when it comes to godly powers. So then, perhaps this is some small bit of Poseidon, exploring the world of man and mortality-- not unlike Jesus-- with the whole of Poseidon back home in his underwater palace.
Again though, why King of Athens, after Poseidon lost out on the patronage of that city to Athena? It seems to me more likely Poseidon would be interested in spiting them than blessing them with a great hero, after something like that. This is something we've seen over and over again. The entire Trojan War is based off of a grudge match between the goddesses who Paris did NOT choose looking to take revenge on the entire city of Troy for the insult. And the fall of Crete can also be attributed to Poseidon teaching Minos a hard lesson for breaking trust and not giving the beautiful gift of a bull back to the gods in sacrifice as he promised.
I suppose Poseidon might have simply possessed Aegeus for the duration of his conjugal visit with Aethra, but I've never heard of another god taking over the body of a man in spirit, when he wanted to get it on, and if he did so, how would that have any effect on Theseus' paternity?
I can definitely see the author's point, regarding Aegeus' associations and his general sea-like presence, but I'm just not sure it takes into account everything else that we know about Aegeus, his relationship to Athens, Poseidon, and the behaviors of the gods. It does not seem consistent with the rest of the myths I've read by any means-- though perhaps I'm just reading too much from an historical viewpoint, with the assumption that these people, in some manner, lived, or must follow some internal logic. After all, if it is all just a story told around the hearth-fire, then why does it have to be anything but what it is? But if myth comes from some kernel of truth, if myth is the cultural memory of gods that have been given up for dead, no less true than any other religious story which we take as history now (like the birth of Jesus as an historical figure), then I need some more convincing than an association with Apollo and his association with the sea.
Morford, Mark P.O., and Robert J. Lenardon. Classical Mythology: Seventh Edition. New York: Oxford University Press, 2003.