if all the Ulema’’ agree on one view...

if all the Ulema’’ agree on one view, then that view is right, because if it had been wrong then the silence of the infallible Imam about it and his not revealing the truth would be evil, rationally. Thus the evil of the Imam's remaining silent about an error, guarantees the rightness of the view universally agreed upon.

Philosophy: This did not become a source of inspiration for thinking on ‘ Ilm’ul Usul on a wide scale until almost the third era, when philosophical studies instead of studies on ‘ Ilm’ul Kalam became widespread in the sphere of Ja'fari theology, and with the spread of important and original philosophies like that of Sadruddin Shirazi (d. 1050A.H.).

This led to the acceptance of the thinking on ‘ Ilm’ul Usul in the third era, with the help of philosophy and through its inspiration (which was greater than the inspiration received by Sadruddin Shirazi.

Examples of this are the question of the genuineness of Being and the genuineness of Essence in a number of problems in ‘ Ilm’ul Usul which he advanced, like the question of the combination of a command and a prohibition and the question of the connection of commands with natures and individuals, on which indeed we cannot elaborate.

The subjective context in which the thinker on ‘ Ilm’ul Usul lived: The specialist on ‘ Ilm’ul Usul lives in a specific context, and derives some of his ideas from the nature of that context.

The example of this is that of those Ulema’ who lived in the first era and found the clear proofs of the Shari’ah easy for them in solving whatsoever needs and propositions they confronted owing to the proximity of the age to that of Imams and the relative paucity of legal problems which they had to face is specific context of theirs and their obtaining proofs made them feel that this state of affairs was absolute and would be the same for all ages.

On this basis they claimed that it is part of the subtlety ( al-Lutf ) binding on Allah that He should provide a clear proof for every law of the Shari’ah , as long as man is Mukallaf (i.e. a legally responsible individual) and as long as Shari’ah continues to exist.

The factor of time: by this is meant that as the separation in time between the thing on ‘ Ilm’ul Fiqh and the age of the promulgation of the authentic texts of the Shari’ah increased and extended, new difficulties arose, requiring ‘ Ilm’ul Usul to study them.