Learn Turkish: Yolculuk çok kötüydü, otobüste uyuyamadım. - The journey was very bad, I could not sleep on the bus.

It is built like this: uyu (sleep) + y (buffer letter) + ama (unable to) + dı (past tense) + m (I). Because the verb root uyu ends in a vowel and the inability suffix -ama starts with a vowel, we must put the buffer letter -y- between them.

Why does "kötüydü" (it was bad) have a "y" in the middle?

The word kötü (bad) ends in a vowel. When you attach a past tense ending directly to a noun or adjective that ends in a vowel, you must use the buffer letter -y- to connect them. So we get kötü + y + dü.

Why is the ending on "otobüste" (on the bus) spelled with a "t" instead of a "d"?

This is because of consonant mutation. The word otobüs ends in the hard consonant "s". When a suffix that normally starts with "d" attaches to a hard consonant, it changes to "t" to match the hard sound. So the location suffix -de (in/on/at) changes to -te.

Why does the past tense part of "uyuyamadım" use "dı" instead of "di" or "du"?