Is blind adherence to the jurisprudential schools of thought permissible, or must the follower adopt what he is convinced by, and what is the difference between that and Ijtihad?

It is not permissible for a mujtahid (independent jurist) to engage in taqleed (imitation/following a specific school of thought); rather, he acts according to what he finds to be preponderant based on the Sharia evidence. As for one who is able to weigh between evidences, it is incumbent upon him to act according to the strongest among them, regardless of the madhhab (school of thought). This rank, between ijtihad and taqleed, is called "discernment" or "following," in accordance with the Almighty's saying: (So give tidings to My servants those who listen to the Word and follow the best of it. Those are the ones whom Allah has guided, and those are the ones possessed of understanding). As for the layperson (‘ammi), it is permissible for him to follow a specific madhhab or not to follow one, and he should ask trustworthy scholars about what is unclear to him, without requiring knowledge of the evidence, based on the Almighty's saying: (So ask the people of the message if you do not know). It is preferable for him to ask about the evidence if it can be explained to him. The blameworthy taqleed is clinging to falsehood by imitating sheikhs and forefathers.