What is the difference between bidʻah (innovation) and mursalah maslahah (unrestricted public interest)?

Summary: Innovation (bid'ah) is defined as every newly introduced matter attributed to religion without a legal basis. Its pillars consist of: innovation, its attribution to religion, and its lack of reliance on a legal basis. As for unrestricted public interest (maslahah mursalah), it is a benefit for which no specific evidence has been transmitted regarding its consideration or annulment.

Points of Agreement between them: 1. Both were mostly unknown during the era of prophethood. 2. Both lack specific, particular evidence.

Points of Difference between them: 1. Innovation (bid'ah) is only in matters of worship, whereas unrestricted public interest (maslahah mursalah) is in matters whose meaning is rationally understood. 2. Innovation (bid'ah) is intended as a primary objective, and its adherents often seek closeness to God through it, whereas unrestricted public interest (maslahah mursalah) falls under the category of means and is intended as a secondary objective. 3. Innovation (bid'ah) ultimately leads to imposing hardship on the accountable, whereas unrestricted public interest (maslahah mursalah) results in ease. 4. Innovation (bid'ah) contradicts the objectives of Sharia, whereas unrestricted public interest (maslahah mursalah) falls under them and serves them. 5. The non-occurrence of unrestricted public interest (maslahah mursalah) during the era of prophethood was due to the absence of a prompting factor or the presence of a preventing factor, whereas the non-occurrence of innovation (bid'ah) was despite the presence of a prompting factor and the absence of a preventing factor.

Accordingly, if unrestricted public interests (masalih mursalah) adhere to their conditions, they are contrary to innovations (bida') and distinct from them, and the emergence of innovation from their direction is prevented.