والكلمة والكلام لعلم النحو
The word and speech are the subjects of grammar.
Grammar considers expressions in relation to inflection, construction, and the roles of sentence elements. It does not automatically turn every historical or phonetic fact about a word into a grammatical issue.
In كَتَبَ زَيْدٌ الدَّرْسَ, identifying Zayd as the agent and al-dars as the object is a grammatical inquiry. This illustrates why knowing the subject must be combined with knowing which properties are being investigated.