Among major discussions of practical principles in Shiite “principles of Jurisprudence” is the principle of Occupation (or precaution) which is used when one is certain of the existence of the compulsory task but has some doubt about what he has been commended to do or to avoid. This practical principle cannot be found in the books of carlier Usulis being separated from “the principle of prohibition”. The present essay pursues the issue from the earliest Shiite Usuli Books (in which no trace of the said principle can be found) and goes further and further in order to expound the gradual generation of this principl. It finally indicates that the starting point for the general notion of “doubt” and “practical principles” wherein the principle of occupation or precaution is discussed is innovated by al-shaikh al-Ansari and then adapted and enriched by all other Shiite Usulis.
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