Learn Turkish: Festivalde yoruluruz diye iki tane katlanabilir sandalye aldım. - I bought two foldable chairs in case we get tired at the festival.

Both can be used for precautions, but they have a slightly different nuance. Using the aorist (yoruluruz diye) frames the precaution as an internal thought or worry: 'thinking we might get tired'. Using the conditional (yorulursak diye) sounds slightly more objective, like 'in the event that we get tired'. However, in everyday speech, native speakers use both interchangeably for 'in case'.

The first verb is 'we' (yoruluruz) but the main verb is 'I' (aldım). How does diye connect different subjects?

Because diye originally comes from the verb demek (to say), it acts like a quotation mark for your thoughts. You are essentially saying: I bought two chairs, thinking 'we might get tired.' Since it quotes the exact thought running through your head at the time, the subject inside the diye clause doesn't need to match the subject of the main sentence.

How is the adjective katlanabilir (foldable) formed grammatically?

It is built using the aorist participle. It starts with the passive verb katlanmak (to be folded), adds the potential suffix -abil (can/able to), and ends with the aorist suffix -ir. Just as English uses '-able' to show capability, Turkish uses the aorist of a potential verb to make adjectives. Another common example is sürdürülebilir (sustainable).

Could I use instead of to express 'in case' here?