AspectFardWajibEvidenceDefinitiveSound but non-definitivePerformanceBindingBindingAssentAcknowledgment of a definitive obligationThe same categorical degree is not requiredOmissionUnjustified neglect is impermissibleUnjustified neglect is impermissible
The decisive difference concerns certainty of proof, not permission to disregard wajib. It is therefore mistaken to call every binding act technically fard or to assume that anything not fard is voluntary.