IÇ-DÜNYA
Qalb · Fuʾād · Ṣadr — The Three Inner Centers
The Qur'an does not name the human 'inner' with a single word. There are three distinct names, each indicating a different layer: ṣadr is the outermost, qalb the middle, fuʾād the innermost. Their alternation is not random — each choice specifies which layer the divine message is addressing.
الصَّدْر
Ṣadr
ṣ-d-r (to come forth)
The breast — the outer layer surrounding the heart. The stage of emotions and outward reactions: constriction/expansion is lived here (as in 'We expanded your breast' of al-Sharḥ).
اَلَمْ نَشْرَحْ لَكَ صَدْرَكَ
Did We not expand for you, [O Muhammad], your breast
— İnşirâh 94:1
USAGEThe Qur'an speaks of ṣadr in matters of 'social engagement,' 'expansion of the chest' (sharḥ), and 'constriction' (ḍīq).
القَلْب
Qalb
q-l-b (to turn, invert)
The heart — the middle and central layer. Faith, reason, intention, decision settle here. The very name 'qalb' means 'that which continually turns': faith is open to drift, sealing, cleansing.
اِنَّ فِي ذٰلِكَ لَذِكْرٰى لِمَنْ كَانَ لَهُ قَلْبٌ اَوْ اَلْقَى السَّمْعَ وَهُوَ شَهِيدٌ
Indeed in that is a reminder for whoever has a heart or who listens while he is present [in mind]
— Kaf 50:37
USAGEFor the qalb the Qur'an uses expressions of both disease (maraḍ), guidance (hudā), and sealing (khatm) — the human's inner destiny is decided at this level.
الفُؤَاد
Fuʾād
f-ʾ-d (to burn, kindle)
The inmost heart — the deepest, most 'burning' center. The place where revelation directly descends, the witness the consciousness holds. 'The fuʾād did not lie about what it saw' (Q 53:11) — here it is the fuʾād that 'sees.'
مَا كَذَبَ الْفُؤٰادُ مَا رَاٰى
The heart did not lie [about] what it saw
— Necm 53:11
USAGEFuʾād appears rarely (~16 times) in the Qur'an but in critical places: reception of revelation, love for the Kaʿba (Q 22:32), Mary awaiting her son (Q 28:10).
THE NUANCE
In al-Sharḥ, 'Did We not expand your ṣadr?' — the outer layer. In Qāf, 'a reminder for one who has a qalb' — the center. In al-Najm, 'the fuʾād did not lie about what it saw' — the innermost. When the Qur'an selects a layer, it selects the addressee's layer.
Source: Ibn Qayyim, *al-Tibyān*; al-Rāghib al-Iṣfahānī, *al-Mufradāt* (entries *q-l-b*, *f-ʾ-d*, *ṣ-d-r*).