The fact is that there are several nouns that are sufficiently irregular that one needs to memorize their declensions; among these are the kinship words: ἀνήρ, γυνή, μήτηρ, πατήρ, θυγάτηρ; then there are ναῦς and βασιλεύς and πόλις. I used to introduce these nouns -- and the heteroclitics like υἰός/υἱεύς, etc. -- and make it an occasion for talking about the phonetic and orthographical factors in play -- what I call "the archaeology of Greek morphology". Of course, understanding the "archaeology" doesn't free one from the obligation to know the paradigms of these "irregular" nouns, but I always thought it easier to get a grip on them by understanding how those apparently anomalous forms emerged, e.g. the δ of ἀνδρός where the root is ἀνερ-, or the α of the dative plurals πατράσι, μητράσι, ἀνδράσι.
οὔτοι ἀπ’ ἀρχῆς πάντα θεοὶ θνητοῖς ὑπέδειξαν,
ἀλλὰ χρόνῳ ζητέοντες ἐφευρίσκουσιν ἄμεινον. (Xenophanes, Fragment 16)
Carl W. Conrad
Department of Classics, Washington University (Retired)