Abstrakt
The past perfect of Old Polish verbs was a compound tense that was formed in 3. singularis masculini by combining the active past participle (participium praeteriti activi) ending with -ł and an auxiliary verb jest, for example niosł jest. In the 15th century, the auxiliary verb jest was already advanced in perishing. As a result of this process the active past participle ending with -ł (for example niosł) became equal with 3. singularis masculini praeteriti niosł. A contemporary researcher of Old Polish faces huge difficulties with noticing the problem at all as well as with establishing a proper form of a given verb. The article describes problems in this area and methods of solving them.