The meaning of consensus, in the terminology of Fiqh people, is the agreement of all Muslims or all people of knowledge on a religious law which, according to the opinion of those who believe in it being the proof, proves the religious law; because the agreement of all Muslims or all people of knowledge on falsehood is not possible, and this is true due to the credit of existence of the God’s Caliph among them; as God has said: ﴿وَمِمَّنْ خَلَقْنَا أُمَّةٌ يَهْدُونَ بِالْحَقِّ وَبِهِ يَعْدِلُونَ﴾; “And from those whom We have created there always exist a group who guide toward the truth and thereby administer justice upon it!” and with this description, the agreement of them all on falsehood is impossible; except that such an agreement is neither discoverable nor useful, because on the one hand, counting the opinion of them all is not habitually possible, and on the other hand, what they all consider proved, does not need to be proved so that for proving it, one cites the agreement of them all. It is understood from here that the impossibility of proving the religious law by consensus is from the viewpoint of the whole subject rejection, considering, one the one hand, the impossibility of complete induction, and on the other hand, the impossibility of acquiring what is already acquired, and the intention of his Honor Allamah about the lack of proof of consensus is nothing except for this.
But “the consensus of a group of experts”, regardless of it is about what law, is a contradictory interpretation; because the agreement of “a group of experts” is not called consensus, rather the agreement of them all is called consensus, and such an agreement, whether is about a legislative law or a creational law, is not attainable. Yes, “the consensus of a group of experts” with the meaning of knowing the opinion of most of them, and lack of knowing the opposite opinion, is attainable, but it is not sufficient to prove any law, although it would be creational; as “a group of experts” for hundreds of years have agreed over flatness of the earth and the sun’s rotation around it and the existence of four elements and the nine heavens and the seven regions in the universe, and there was not any known opposition for their opinions, and yet their incorrectness was revealed.
But it is not obligatory to refer to the Caliph of God for knowing the creational laws such as engineering, techniques, agriculture, economics and medicine; because these laws have actual and natural essence, and the actual and natural laws are being known through intellect, except in some aspects of them which have legislative laws, such as the law of tall constructing of buildings and constructing toilets towards Qibla, the law of metayage and sharecropping, and the law of usury, and some businesses and the law of doctor’s responsibility. Considering such a condition, referring to the Caliph of God is also very helpful in understanding the creational laws, but it is not unlikely that many of these laws have been taught by the God’s Caliphs; as for instance, it has been narrated that the first person who composed a poem was Adam peace be upon him, The first person who wrote with the pen was Idris peace be upon him, and he was also the first person who sewed and wore clothes and those who preceded him wore animal skins and it has been said: God taught him astronomy, arithmetic and geometry, and It has been narrated that the first person who built a ship, that was floating on water, was Noah peace be upon him, and the first person who arranged the army in battle into three parts: right, left, and middle, and arose flags was Ibrahim peace be upon him, when he moved toward fighting with those who had captured Lot peace be upon him, and he was the first person who made shoes, and the first person who rode the horse was Ismail peace be upon him and before him the horses were wild and did not let riding, and the first person who built the scale and balance was Shuaib peace be upon him, and the first person who built the armor was David peace be upon him, formerly it was like the connected sheets, then he weaved it into the ring-like shape to be both lighter and firmer, and the first person who made sugar was Solomon peace be upon him and he was the first person for whom a mixture of lime and orpiment was made and went to the bathroom, and the first person who built dam on the earth was Dhul-Qarnayn.