Whether you describe a glass as half full or half empty is the classic shorthand test of temperament. The glass and its contents are identical either way; what differs is the person looking at it. The optimist notices what is there, the pessimist notices what is missing. From the question grew an adjective: a ‘glass-half-full person’ is a habitual optimist, a ‘glass-half-empty person’ the reverse. The image is often used gently against pessimists, but strictly speaking both descriptions are accurate, which is rather the point.
What’s the origin of the phrase ‘glass half full’?
The glass came before the optimism. The earliest known form of the idea is a piece of wordplay rather than a comment on character. In December 1908 a Minnesota newspaper printed a paradox credited to David Dodge of The New York World, in which a fictional Professor Nix observes: “You see this glass of mine is half full; yours is half empty, but both contain the same amount of water.” No optimists or pessimists in sight; just the observation that the two descriptions are interchangeable.
The temperament reading arrived later, and in American papers it began as a motoring joke. The Evening Sun of Baltimore ran this unattributed filler item in April 1929: “If he says his gas tank is half-full he’s an optimist. If he says it’s half-empty he’s a pessimist.” Gas-tank variants bounced around US newspapers through 1929, and by 1931 a Chicago paper was running the same gag about a half-full (or half-empty) bottle.
The man most often credited with the saying is the British economist Josiah Stamp. Addressing the Society of Incorporated Accountants and Auditors in London in April 1935, he was reported by The Daily Telegraph as saying: “An optimist is the man who looks at his glass and says it is half full. The pessimist is he who looks at it and says it is half empty.” Stamp gave the line its most quotable outing, but he was polishing a joke already in circulation, and the quotation researcher Garson O’Toole, who assembled the citations above, concludes that the originator remains anonymous. Ronald Reagan is another name the line is sometimes hung on; that belongs to the phrase’s later life, not its birth.
By the late twentieth century ‘is the glass half full or half empty?’ was a fixture of speeches, self-help and job interviews, and the adjectival forms had settled in alongside it. Comedians have kept amending it, the standard modern rejoinder being that the glass is simply twice as big as it needs to be. As folk optimism goes it pairs naturally with every cloud has a silver lining, though the glass version is unusual in giving the pessimist equal billing.