To talk about something that did not happen but you wish had, add -se/-sa to the verb stem, then -ydi and the person ending; keşke in front makes it a regret. The other half of the sentence usually takes -irdi or -ecekti.
Examples
- Keşke ailemle daha çok zaman geçirseydim.
- I wish I had spent more time with my family.
- Gençken bunu bilseydim, hayatım değişirdi.
- If I had known this when I was young, my life would have changed.
- Keşke ona gerçeği söyleseydin.
- I wish you had told him the truth.
The mistake to avoid
Keşke needs the -seydi form; a plain past tense after it ("Keşke söyledin") is wrong.
Where this fits in
Hayat üzerine düşünceler, Turkish B2: Reflect on life, values, personal growth, and relationships.