The introduction also addresses the position of the conclusion:
وَجَعْلُ الْخَاتِمَةِ خَارِجَةً عَنِ الْفَنِّ الثَّالِثِ وَهْمٌ
It is a misconception to treat the conclusion as outside the third discipline.
A section called a 'conclusion' does not necessarily fall outside the third discipline simply because of its heading. Its disciplinary location depends on its subject matter.
Accordingly, a concluding portion of a discipline is not automatically a separate fourth discipline. This resolves a possible misunderstanding in the book's overall structure.