«وَتَبَايُنُ الْأَسْبَابِ لَا يَضْبِطُهُ الْحَصْرُ»
The variation of the causes cannot be exhaustively enumerated.
Habits, circumstances, education, social practices and past observations differ among people. It is therefore impossible to provide one fixed list of every circumstance that makes two images mentally co-occur.
This matters for waṣl: mastering the definition of jāmiʿ is insufficient unless one can explain how the intended audience would associate the particular representations.