Simplify the following text for a Grade 10 native English-speaking person.
Original: Often doctrine specifically connotes a corpus of religious dogma as it is promulgated by a church , but not necessarily : doctrine is also used to refer to a principle of law , in the common law traditions , established through a history of past decisions , such as the doctrine of self-defense , or the principle of fair use , or the more narrowly applicable first-sale doctrine .
Simplified: Doctrine often means several religious dogmas that a church teaches . But it can also mean a principle of law , in the common law traditions , established through a history of past decisions , such as the doctrine of self-defense , or the principle of fair use .