How can the Usuli principles not based on direct texts from the Quran and Sunnah be applied in legislation?

The sources of Islamic legislation are the Qur'an and the Sunnah. The usuli (juristic-legal theory) and fiqhi (juristic-legal) rules are derived from them, either verbatim or in meaning. Rules such as: "Actions are but by intentions" and "There shall be no harm or reciprocating harm" are found verbatim in authentic hadiths. As for rules such as: "Necessities permit the prohibited" and "Difficulty brings ease," they are derived from the meanings of noble verses, such as His (Allah's) saying: "And He has already explained to you what He has forbidden to you, except for that to which you are compelled" and "and has not placed upon you in religion any difficulty."