A principle is a comprehensive and fundamental law, doctrine, or assumption, the idea of which being a central one in Western thought. For example the action of "change" is said to be based on five principles.
Commonly used synonyms for principle are (originative) "source" or "beginning".
For example, in some senses a "nature" or "subsistence" is the source of a thing's action, a "substance" is the source of a thing's materiality and an "essence" is the source of a thing's being. And there are "accidental" principles that are not the source of a thing's properties but are simply able to co-exist as a source of something in the principled subject. Likewise, there must be "non-accidental" or what might be called "propertorial" principles that are consequential on the existence of a thing in and of itself.
Principle, cause and element
A "cause" is a kind of principle, but the meaning of principle can be broader than "cause" in at least two ways. Firstly, a principle can be a "privation" in the sense of the absence of a thing understood to be present by nature. Thomas Aquinas describes this as an "accidental principle". An example could be the absence of a woman's eye, of which could be spoken as a principle of a prevention of a cause, like in a police investigation.
An element or component or part is a kind of principle, which can always be a material cause; sometimes a final cause or end or an efficient cause or means; but never a formal cause (because the form into which a thing is caused to be must be a unity unless understood to be divisible, and if acting as such, the form is not the essential form of the thing, but the dividends are able to be considered separately with their own set of other causes).
So there is a kind of hierarchy of the ideas of principle, cause and element.
Three types of principles
Principles can be divided along three primary types: principles of reality, moral principles and logical principles. Principles of reality may more commonly be called "principles of nature", but since there are definitions of "nature" that might call it a kind of principle itself, its use might be better avoided.
- "principle" (June 2006 or bef.) The Merriam-Webster.com Dictionary (Unk. city: Merriam-Webster).
- "[T]hough privation is an accidental principle, it does not follow that it is unnecessary for generation." Aquinas, St. Thomas (1255). De principiis naturae in Bourke, Vernon J. ed. and transl. (1960). "Principles, causes and natural generation". The Pocket Aquinas (New York, NY: Washington Square Press/Pocket Books), pp. 61-77, transl. from Pauson, J., ed. (1950). On the Principles of Nature (Fribourg [France]: Société Philosophique, 1950).
- Aristotle (c. 350 B.C.) Categories (Athens, GR) in Hutchins, Robert M., ed. (1952). "Categories". Works of Aristotle, vol. 1 in Great Books of the Western World, 2nd ed. (Chicago: Encyclopaedia Britannica, 1954), vol. 8, p. 17.