«أَوْ تَمَاثُلٌ»
Or similarity between the two.
Tamāthul means that two things remain distinct while resembling one another in some relevant kind or characteristic. Two writers, for example, may share a recognizable professional activity, or two scholars may work in a common discipline.
The statement that both things merely 'exist' or are 'physical' may be too broad. Effective coordination calls for a similarity genuinely relevant to the discourse.