وهو علم أي ملكة يقتدر بها على إدراكات جزئية
It is a science, that is, a settled faculty enabling one to grasp particular cases.
A malaka is a developed intellectual competence. General principles support it, but memorizing rules is not the same as applying them to an actual utterance. The source's discussion connects the abstract discipline to judgments about particular expressions.
Someone may recall the definition of emphasis yet fail to use it appropriately with a doubtful or opposing audience. Such a person has information but not the full practical competence.