A rational relation may involve likeness or correlative terms, such as father and son, whose meanings are relational. By contrast, imagined association can invoke a counterpart through opposition or near-opposition.
هَذَا أَبٌ وَهَذَا ابْنٌ.
This is a father, and this is a son.
حَضَرَ الْغَنِيُّ وَجَاءَ الْفَقِيرُ.
The wealthy person was present, and the poor person arrived.
The first highlights correlation; the second contrasts social conditions. Mere appearance of opposite words does not by itself decide whether two predications should be coordinated. Syntax and discourse purpose remain decisive.