The Eight Noun Rules (BBG Appendix ~p.344)

1. Stems ending in α,η are 1st declension, stems ending in o are 2nd, consonantal stems are 3rd
2. Neuters are always the same in Nominative and Accusative
3. Almost all neuter plurals end in -α in the Nominative and Accusative Plural
4. Iota always subscripts in Dative singular, if possible (not possible in 3rd declension, since iota only subscripts under vowels)
5. Vowels often change their length (Ablaut)
6. Masculine and Neuter always the same in Genitive and Dative
7. The Square of Stops (See below)
8. Tau cannot stand at the end of a word, and will drop off (ντ + ς = ς)

   The Square of Stops (BBG 10.17-20)

   Type	Voiceless	Voiced	Aspirate	Spirant Double (With Sigma)
   Labials	π	β	φ	+ σ => ψ
   Velars(Palatals)	κ	γ	χ	+ σ => ξ
   Dentals	τ	δ	θ	+ σ => σσ => σ