Uṣūl al-Fiqh

Question: What is the wisdom behind the variation of the evidences of obligatory rulings in terms of clarity and obscurity, strength and weakness, certainty and probability, nearness and remoteness, and so on?

Question: Do legal obligations differ from one person to another due to differences in people’s dispositions or other factors?

Question: When did the science of Uṣūl al-Fiqh appear? And likewise the science of Uṣūl al-Dīn?