The Structure of Islamic Law
Islamic law has three sources: the Koran, the hadith and the law doctors.
1) THE KORAN: Alleged revelation from God to angel Gabriel to the prophet Mohammed, to the people, contemporary and subsequent.
Equivalent to the Torah (or Tanakh); it is the founding scriptures, the ultimate reference document for Islamic law.
For Mohammed: granting his sincerity, how can he be sure the vision and voice of Gabriel was not a hallucination. How can he be sure his “Gabriel” is a messenger from God, and not a visitor from some other planet, say.
For his disciples and followers: how to be sure of Mohammed’s sincerity (i.e. that it was not all a trick of his to gain power and influence) and accuracy (i.e. that he did not simply hallucinate).
Note also that, according to Arnaldez, the Koran has so far not been subjected to historical and textual criticism by impartial researchers.
The recipients of an alleged revelation have to learn to distinguish between:
a) The appearance of sights and sounds to the alleged prophet — X.
b) The verbalization of the phenomenon — “X occurred”
c) The identification of God as the source of the phenomenon — “X was from God”.
d) The taking into consideration of the recipient of the message — “Mohammed considered that God gave him the message X”.
The alleged event (a) and the various propositions about it (b, c, d) cannot logically be treated as equivalent, as naïve readers of revelations tend to do. (d) does not necessarily imply (c), (b) or (a). The transition from each to the next involves a conceptualizing or rational act of a human mind, and is subject to possibilities of error of observation or verbalization or causal logic. This is true of any revelation, not just the Islamic.
2) THE HADITH: Alleged eyewitness accounts of the sayings and doings of the prophet, supposedly written down by his contemporary followers, for their successors. Some hadith were apparently transmitted orally. Some have been judged authentic (sahih), others less so (hasan), still others forged (saqim).
Serves as second level of reference for Islamic law. Thus, technically equivalent to the Oral tradition of Judaism (written in the Mishnah and Gemara), though less spread out in time and therefore more likely to be a reliable report.
For the eyewitnesses: granting their sincerity, how can they be sure their observations of Mohammed’s actions were properly remembered and relevant.
An item X may be a broad law; Mohammed’s action represents one possible concrete application of that law (he has to apply it somehow); but there may be other acceptable concretizations; the simple fact that Mohammed chose a given one, though legitimizing, does not in itself exclude other conceivable concretizations. To make Mohammed’s actions equivalent to law is to imply he received more instructions than he transmitted, and to make a wrong generalization from his actions.
With regard to verbal pronouncements by Mohammed reported by others: they may have been improperly remembered; and even if they were written immediately (though not verbatim), they may have been improperly understood and reported.
Similar problems, and more, occur with regard to Jewish tradition. A rabbi may perform a mitzvah in a certain way, because he has to do it some way, not because it is the only way; yet his disciples take it and transmit it as the way; and so it remains if uncontradicted. If a rabbi says something, his disciples likewise will assume it of traditional origin and descent; but it may in fact be his own interpretation, or he may have misunderstood what his teachers said or did, or he may have badly remembered and filled in blanks, and so forth.
For the subsequent generations: they may doubt the sincerity of the eyewitnesses, or their accuracy of hearing or observation, or their having been eyewitnesses at all, or the authenticity of the text received. It is important to resist the tendency religion induces in us all to be credulous to events or claims that are far away in time and therefore almost unverifiable!
We can here, as above, express the transitional problems in formal terms: that “Alleged eyewitnesses claim they saw or heard Mohammed doing or saying Y” does not prove that “M did/said Y”, nor that “What Mohammed did/said was divinely approved or intended”. It is naïve to regard these propositions as equivalent, each one involves further assumptions than the next.
3) THE LEGAL EXPERTS: those who try to develop a precise jurisprudence, with reference to Koran and hadith, resolving contradictions, making clarifications and inferences, filling in blanks, extending laws to new situations.
Here, reasoning is at stake, just as in the Talmud and subsequent rabbinic writings (formal issues, in addition to alleged traditions as to content). Initially, personal opinion (ray) of Islamic masters was legitimate; eventually, traditionalists reacted with more stringent demands. Their hermeneutics, which have some resemblances to the Judaic, may similarly be subjected to critical review.
 Roger Arnaldez, L’Islam (Paris: Desclée/Novalis, 1988), p.196.