You know you can only conjugate verbs.

Ex: gider -im (personal ending for first person)

      gider -sin (personal ending for second person)

      gider - 0  (no personal ending for third person)

But it looks like we also conjugate nouns.

Ex: güzel -im

      güzel -sin

      güzel

But it is not as it seems. Because we actually conjugate a hidden verb not the noun. That verb is "ermek". It means to be, to exist. In time this verb changed like this:

er(mek) - e(mek) - i(mek) and then it dissappeared. But actually it is still there. Sometimes it is hidden in the personal ending and you can´t see it but sometimes you can make it appear.

Ex: güzelmişsin : güzel -i-miş-sin. Now you can see it.

What I want to say is  we also don´t conjugate nouns in Turkish. But it seems so.

This "i" also obeys to the vowel harmony.

Ex: hasta-ı-mış-ım