In a nutshell they arise naturally from the Arabic language and the Islamic sources and the experience we bring to bear in understanding them.
An example will help to explain. It is narrated when the Prophet (saw) decided to fight the Jewish tribe of the Banu Qurayzah following their treachery in the battle of the trench (khandaq), he instructed his troops, "Do not pray the asr prayer except in the abode of the Banu Qurayzah."
The companions marched off to battle. En route the time arrived for the asr prayer and the companions differed in their understanding of the prophet's command. Some took it to mean that they should pray the asr prayer when they reached the Banu Qurayzah, even if this meant praying it after its prescribed time. Others believed the Prophet meant they should not waste any time in setting off to the battlefield, namely they were being requested to hurry, but were nonetheless supposed to pray the asr prayer at its due time. When they returned the Prophet (saw) was consulted and the alternative understandings explained - he remained silent on the matter. He did not reprimand either group, nor did he endorse one understanding over the other. This narration is a classical example to which Muslim jurists have regularly referred to demonstrate two points: - The first is that differing conclusions could arise from sound ijtihad, the effort made by jurists to discover God's law in any given case. Since the Prophet did not tell either group they were wrong, it must have been the case neither was.
- Secondly, this report illustrates the difference between "literalists," viz. those who adhere to the "letter" or "apparentness" of written or verbal commands compared to those who pay more attention to the objectives (maqasid) which commands and laws in general, seek to realize.
Arguably, the latter understanding fared much better in Islamic legal history than the former; however, the former has not been categorically dismissed, for a report like the one mentioned above lends credence to this mode of thinking. Just as some of the prophet's companions were more interested in the objectives of the Prophet's (saw) command, others were more interested in obeying its letter. Both groups were sincere, even if they proceeded along differing lines.