Learn Turkish: Fark ettim ki kapı kilitliydi. - I noticed that the door was locked.

It is because of the conjunction ki! When ki is used for realization, it joins two separate, complete sentences exactly like the word "that" does in English: Fark ettim (I noticed) + ki (that) + kapı kilitliydi (the door was locked). This is a rare exception to the normal Turkish word order, making it very friendly for English speakers.

Why is the past tense in fark ettim spelled with a double "t" instead of a "d"?

The action word here is the compound verb fark etmek (to notice). To make etmek past tense, you usually add the suffix -di. However, because etmek ends in the hard, voiceless consonant "t", the "d" in the suffix hardens into a "t" to match it. Add the personal ending -m for "I", and et-di-m naturally becomes ettim.

How do the suffixes build the word kilitliydi?

It starts with the noun kilit (lock). First, the suffix -li (meaning "with" or "having") is added to make the adjective kilitli (locked). Finally, to say "was locked", we add the past tense suffix -di. Since kilitli ends in a vowel, the buffer letter -y- is needed to keep the vowels apart, resulting in kilit-li-y-di.

Is it possible to say this sentence without using ?