مَا عِنْدَكَ؟
What do you have?
مَنْ فِي الدَّارِ؟
Who is in the house?
The first question may seek the kind of thing, answered 'a book.' The second seeks the person, answered 'Zayd.' The difference is not merely in the wording of the replies; the interrogative directs attention to a different kind of missing information.
Distinguish grammatical or linguistic kind, the technical logical genus, and personal identification. Not every mā-question demands a complete definition, nor must every man-question be answered by a proper name.
QuestionInformation requestedPossible answer
Mā ʿindaka?What item or kind?Kitāb
Man fī al-dār?Which person?Zayd
Mā al-kalima?Nature or classes of the wordNoun, verb or particle