How did Senate resolutions become a source of law during the early Roman Empire?

During the early Roman Empire, the status of senatus consulta (resolutions of the Senate) shifted significantly from advisory suggestions to a formal source of law.1

During the Republic, the Senate’s decrees were merely advisory and lacked legislative force, though they were often implemented by magistrates. As the power of the popular assemblies declined under the early emperors, the Senate became the primary body for endorsing the emperor's proposals.12

The transition occurred as follows:
* Imperial Mouthpiece: Early emperors used the Senate as a vehicle for their own legislative agenda, issuing laws in the form of senatorial decrees.3
* Binding Authority: Although these decrees were not initially termed "laws" in the formal sense, they were treated as binding.4
* Automatic Approval: As the emperor’s position strengthened, the Senate’s approval of his proposals became increasingly automatic. By the 2nd century CE, the Senate often ceased to draft its own legal language, instead repeating the emperor's speeches verbatim.13

Eventually, as the emperor became the sole creator of law, the practice of legislating through the Senate was abandoned in favor of direct imperial constitutiones principum.13