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Every thing has an intrinsic nature or essence—properties that make it what it is and are constitutive of its identity. Understanding essence is crucial for identity criteria, definition, and natural kinds. Some properties are essential (a triangle must have three sides), while others are accidental.
Begin with clear cases of essential properties (mathematical definitions) then examine contested cases (is being rational essential to humans?). Consider how essence relates to necessity and possible worlds.
That essence is unscientific or purely linguistic. That all properties are equally essential or equally accidental. That essential properties must be obvious or knowable a priori.
From your study of essentialism and accidentalism, you know the basic distinction: some properties are essential to a thing (it couldn't exist without them) and others are accidental (it happens to have them but could lose them and still be the same thing). The concept of essence or intrinsic nature deepens this: essence is not just a list of essential properties but the constitutive character of a thing — what makes it the very thing it is, as opposed to something else.
A triangle must have three sides — this is an essential property. But it's more than that: three-sidedness is partially *constitutive* of what a triangle is. You can't subtract it and have a somewhat-diminished triangle; you'd have a different kind of shape entirely. This is why essences show up most clearly in mathematical and logical entities: the essence of a prime number just is being a natural number greater than 1 whose only divisors are 1 and itself. There's no room for accidental variation. Mathematical definitions capture essences precisely.
The philosophical action begins when we move to natural kinds and individuals. Aristotle argued that natural species have essences — the essence of a human being was traditionally given as *rational animal*. Kripke and Putnam, working in modal metaphysics, argued that natural kinds like water and gold have de re essences discoverable by science, not by linguistic analysis: the essence of water just is H₂O, regardless of what ordinary speakers mean by "water." This connects essence to necessary properties across possible worlds — the essential properties of a thing are those it has in every possible world where it exists. If being composed of H₂O is essential to water, then there is no possible world where water exists but isn't H₂O.
Intrinsic nature extends the concept: the intrinsic nature of a thing is the totality of properties it has in virtue of itself, independently of its relations to other things. Being 5 feet tall is intrinsic; being the tallest person in the room is relational. Philosophers dispute exactly how to draw the intrinsic/extrinsic line, but the distinction matters enormously for questions of identity and individuation. When you ask what makes this particular gold atom the kind of thing it is, the answer appeals to its intrinsic nature — its atomic structure — not to its accidental history or relational context. Understanding essence and intrinsic nature gives you the conceptual tools for analyzing identity criteria, natural kind classifications, and the metaphysics of what things fundamentally are.
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