Learn Turkish: Polis ehliyeti kontrol ediyorken şoföre ceza yazdı. - The police fined the driver while checking his license.

The suffix -ken (meaning 'while') doesn't change based on the main sentence's tense. Adding it to the present continuous (-iyor) shows that the action was ongoing at that exact moment ('while he was checking'). The main verb yazdı (wrote) sets the time frame for the whole sentence in the past.

How do we know the police officer is the one checking the license, not the driver?

When you use -ken, the action usually shares the same subject as the main verb unless you specify a different one. Since the main subject who fined the driver is polis, we know the police officer is also the one doing the checking (kontrol ediyorken).

Why is it ehliyeti instead of just ehliyet?

Ehliyet (driver's license) takes the specific direct object suffix -i (the accusative case) because the police officer is checking a specific license (the driver's license), not just licenses in general.

Why is the dative case (-e) used on şoföre?

In Turkish, you literally 'write a fine to someone.' The phrase is birine ceza yazmak. So, şoför (driver) becomes şoföre (to the driver).