When, if, if only: the three conditions
The Qur'an has three conditional particles, and each says how real the condition is: إذا sets what will happen ("when"), إن sets an open hypothesis ("if"), لو sets what is not and will not be ("if …", counterfactual).
The particle إذا does not cast doubt on the event; it fixes its moment: "When the help of God comes, and the victory" (110:1). The help is not a hypothesis; it is announced.
The particle إن opens a possibility without settling it: "And if you are in doubt about what We have sent down" (2:23). The doubt is considered, not asserted.
The particle لو sets a situation that reality has already refuted: "And were they sent back, they would certainly return to what they had been forbidden" (6:28). They will not be sent back; the verse describes what they would do in a world that does not exist.
Two neighbouring uses do not contradict the system:
- the concessive form وَلَوْ ("even if", "even though") stays in the counterfactual or the extreme: "even against yourselves" (4:135);
- the form فَإِذَا of sudden appearance ("and behold") states a sudden fact, therefore a real one: Moussa's staff becomes a serpent (7:107).
For the translator the consequence is simple: إذا is not rendered by "if", and لو is not rendered by a future.
In the text
إِذَا جَآءَ نَصْرُ ٱللَّهِوَإِن كُنتُمْ فِى رَيْبٍۢوَلَوْ رُدُّوا۟ لَعَادُوا۟فَإِذَا هِىَ ثُعْبَانٌۭ مُّبِينٌۭوَإِذَا شِئْنَا بَدَّلْنَآ