The bubble label carries no analytical weight

Calling an asset "a bubble" explains nothing: the word has never been formally defined, is applied by commentators to any price that looks slightly too high, and functions as a label for episodes we lack a better explanation for. This is a live question whenever bitcoin's price history is dismissed as "a bubble" (or defended as "not a bubble") on stage.

For (strongest version as argued): Eugene Fama's position, as summarized in the owner's notes on Quinn and Turner's Boom and Bust: "bubble" is devoid of meaning, having never been formally defined. Media usage supports this — the word gets attached to any asset whose price appears slightly too high, making it a non-explanation of a financial phenomenon.

Against (strongest version as argued): Working definitions exist and do analytical work. Kindleberger's — "an upward price movement over an extended range that then implodes" — is operational after the fact, and Quinn and Turner build a predictive framework on top of it (the bubble triangle: marketability, money and credit, speculation, plus a technological or political spark). The fundamental-value definition (prices disconnected from discounted cash flows) is harder to apply but not empty.

Nuance: Even the definition's defenders concede a bubble can only be identified with certainty after the event, so the label is retrospective, not predictive. For bitcoin specifically, both sides of a debate can cite the same price history: repeated drawdowns fit Kindleberger's implosion pattern, while the fundamental-value test is contested because there is no agreement on what bitcoin's fundamental value is or how to discount it.

Common misstatements: "Economists agree bitcoin is a bubble" (economists do not even agree the word has meaning). "A bubble means the asset is worthless" (historical bubbles attached to durable technologies — railways, automobiles, the internet — where the asset class survived the implosion).