Directional case in Turkish

Directional case suffix is -ra,-re, -eri, -arı  which are indicating the direction.

In modern Turkish these suffixes are NOT functional and  clichéd in few words

and are treated as derivational affix.

dışarı, içeri, ileri, sonra , ora, bura, şura

Today we have dative case suffıx [a,e] that is functional.

iç [internal,inner,interior] + eri ---> içeri [inside, into the interior]

dış [outer,exterior] + arı  -----> dışarı [outside]

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iç  + eri + y + e ---> to into inside

Transformation of suffix -Arı

In old Turkish           =======> -gAru  

 Old Anatolian Turkish ======> -Aru 

 Ottoman Turkish         ======> -Aru

  Modern Turkish          ======> -Arı

So the direction is double marked here. Sort of.

Yes, sort of.

içeri is a noun here

içeri-de

içeri-den

içeri-y-e

içeri-y-i

içeri-nin

So it seems. The noun has eaten the old case marking. It happens a lot.

Yes! As in

han-ım (my khan)

beg-üm (my beg)

hanım-ım = my lady

or ayak kab-ı = shoe

ayakkabı-sı = his/her shoe

In a way all double markings are symptoms of this misunderstanding. Like double possessive suffixes in pronouns (kendisi, birisi) or double passives (konulmak, denilmek). The language community doesn´t seem to perceive the first grammatical marking, so they understand it as a part of the stem and add another one just to make sure.

And historically there must be a lot more about this issue. What was the typical shape of old original stems, one to two syllables? Anything longer must be a mixture of old grammatical (> derivational) markers.