A well-known early classification distinguishes four groups of surahs:
1. Al-sabʿ al-ṭuwal — the seven long surahs.
2. Al-miʾūn — surahs of about one hundred verses or somewhat more.
3. Al-mathānī — surahs generally shorter than one hundred verses.
4. Al-mufaṣṣal — the familiar group of shorter surahs.
This is a classification by relative length and recitational grouping, not a system of assigning exclusive subjects to the four groups. A long surah may contain legal rulings, narratives, and spiritual instruction together; shorter surahs also vary in their thematic content.