«والرابطة هي الحكم بينهما»
And the link is the judgment between the two components.
In a categorical, the copula connects subject and predicate. In a conditional, the relation connects antecedent and consequent. This distinction is fundamental to their logical analysis.
“If water freezes, its temperature will be consistent with the freezing point” relates two propositions through a conditional connection.
Not every conditional in every language must use the exact words “if” and “then,” but these words make the connection easy to see in the source's examples.