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An essential property of a thing is one it must have to be the thing it is — Socrates could not lack humanity and still be Socrates. An accidental property is one it happens to have but could lack — Socrates could have been taller. Aristotle grounded essentialism in natural kinds; Kripke revived it via possible worlds, arguing that natural-kind terms and proper names are rigid designators that pick out the same thing in every possible world. Essentialism shapes debates about species, personal identity, and the semantics of necessity.
Work through Kripke's Naming and Necessity Lectures I and II, paying attention to the thought experiments about identity statements and natural kinds. Then test his conclusions against anti-essentialist critiques by Quine.
You've learned about substance and property — the distinction between a thing and what is true of it — and you may have encountered modal logic's operators for necessity (□) and possibility (◇). Essentialism and accidentalism bring those threads together into a question about the *inner structure* of individual objects: which of a thing's properties does it have necessarily, and which does it merely happen to have? An essential property is one the object could not lack and still be the same object. An accidental property is one it has contingently — it could have been otherwise.
Consider Socrates. He was snub-nosed, Athenian-born, and fond of wine. Could he have been born elsewhere? Could he have preferred beer? Most of us intuitively say yes — these are accidents, features of the particular life he happened to lead. But could Socrates have been a rock? Could he have lacked any capacity for thought or experience? Here intuition pushes back: some properties — perhaps being human, having some biological ancestry, being a minded creature — seem to be ones without which this individual simply wouldn't be Socrates anymore. These are the candidates for essential properties. Aristotle grounded this in natural kinds: a thing's essence is what makes it the kind of thing it is. To understand Socrates essentially is to understand him *as a human being*, not as this particular snub-nosed Athenian.
Saul Kripke revived essentialism in a more rigorous form through the concept of rigid designators. A rigid designator is a term that picks out the same object in every possible world where that object exists. Proper names and natural-kind terms work this way: "Aristotle" refers to Aristotle in every world, not to whoever happens to be the greatest philosopher in any given world. From this, Kripke drew striking conclusions: if Aristotle was necessarily human (given rigid designation and essentialism about biological origin), then the statement "Aristotle is human" is necessarily true — even though it doesn't look like a logical truth. Necessity, Kripke argued, is a metaphysical category, not merely a linguistic one. Things can be necessarily true in reality while being discoverable only through empirical investigation, not pure reason.
The contrast with Quine is instructive. Quine was deeply suspicious of essentialism, arguing that necessity is always relative to a description, never to an object itself. Whether being rational is essential to Socrates depends on which description we use to pick him out — under one description it is, under another it isn't. Kripke's response is that this confuses the *way we refer* to something with *what is true of it*. Once we fix the reference of "Socrates" rigidly, questions about what properties he necessarily has become determinate metaphysical questions — and essentialism gives a principled way to answer them. Whether you find that answer compelling depends on how you weigh intuitions about identity, modality, and what makes something the individual it is.
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