A listener may already know a fundamental fact yet fail to apply its implications to the present case. The speaker may then address that person as though the fact were unknown, using a restricted assertion for correction rather than initial teaching.
For example, someone knows that Zayd bears responsibility, yet attributes a specific decision to other people. “Zayd alone is responsible for this decision” can remind the listener of the relevant consequence of what they already know.
This is expressed in a compact formula:
«قَدْ يُنَزَّلُ الْمَعْلُومُ مَنْزِلَةَ الْمَجْهُولِ»
A known matter may be treated rhetorically as though it were unknown.