DISCLAIMER: I'm not a linguist and I don't have an authoritative source to back my reasoning, so take my answer with a grain of salt. [Grammatical case][1] reflects the grammatical function performed by a word in a phrase, clause or sentence. Noun in a given case (e.g. *úi-ge*) remains a noun and retains its meaning. That gives us multiple good reasons to not treat the word-forming suffixes, like *-siz* as additional grammatical cases: - suffix changes the part of speech, *úi-siz* becomes an adjective (as @AdamBittlingmayer said in the comments); - suffix doesn't reflect the grammatical function of a word in a sentence; - suffix creates a new word, with a new meaning (as @kabraxis said in the comments); - this new word, can have a grammatical case of its own: 1. nominative *úi-siz* - homeless 2. genitive *úı-siz-diń* - of homeless 3. dative *úı-siz-ge* - to homeless 4. accusative *úı-siz-di* - homeless 5. locative *úı-siz-de* - by (at?) homeless 6. ablative *úı-siz-den* - from homeless 7. instrumental *úı-siz-ben* - with homeless It's much more convenient to treat *úi-siz* as a new word than a case of *úi*. [1]: https://en.wikipedia.org/wiki/Grammatical_case