In this talk I will address some methodological issues concerning the investigation of the Old Japanese complement system and its prehistory. Firstly, there are some philological problems with Old Japanese corpus. Secondly, I will argue for a somewhat unusual way of studying complement systems in general. Thirdly, I will show that the previous attempts to deal with the Old Japanese complement system have only been dealing with some of the complement types rather than the whole system. I will then turn to discuss the results of my investigations into the Old Japanese complement system.