One product, many prices
Two people board the same flight. They sit in identical economy seats, breathe the same recycled air, land at the same minute. One paid 90 dollars, the other 410. Nothing about the *thing* they bought differs — only the price. This is price discrimination: selling the same good to different buyers at different prices, for reasons that have nothing to do with what the good costs to provide. The word "discrimination" here is the old, neutral sense of *telling apart*, not unfairness — though whether it feels fair is a real question we will return to.
In the perfectly competitive world from guide one, this could never happen. A price taker facing a sea of rivals must charge the single going price; try to charge one customer more and they simply walk next door. So price discrimination is a clue that we have left perfect competition behind. To pull it off, a seller needs the power to *set* a price rather than accept one — and that is exactly the market power you met when we studied the monopolist. The ability to charge two prices is just market power used more cleverly.
Three conditions that must all hold
Why is most of what you buy *not* price-discriminated, then? Because three things must line up at once, and in many markets at least one fails. First, the seller needs market power. Second, buyers must differ in how much they will pay — what each is willing to part with, their willingness to pay — *and* the seller must be able to tell the groups apart, or at least nudge them to sort themselves. Third, and most overlooked: the cheap buyers must not be able to resell to the expensive ones.
That third condition is why a haircut can be price-discriminated but a bag of rice usually cannot. If a barber gave students a cheap cut, no student could resell the haircut to a banker — a service is consumed on the spot. But if a shop sold rice cheaply to one group, a reseller would buy low there and sell high to everyone else, and the gap would collapse. That reselling-to-erase-a-price-gap is exactly arbitrage, and it is the natural enemy of price discrimination. Sellers spend real effort blocking it: non-transferable tickets, ID checks, region-locked software, "not for resale" labels.
The three degrees, from dream to everyday
Economists sort the strategy into three "degrees," running from a seller's wildest dream to the versions you meet daily. First-degree (or perfect) price discrimination is the fantasy: charge every single buyer the exact maximum they would pay. A used-car haggler who reads your face perfectly, or an algorithm that knows your salary, edges toward it. In the pure case the seller scoops up *all* the gain from trade — the entire consumer surplus that buyers normally keep vanishes into the seller's pocket. It is rare in its perfect form precisely because reading every mind is impossible.
Second-degree is the clever workaround when the seller cannot see who you are but can design choices that make you *reveal* yourself. The menu is the same for everyone; you sort yourself by the version or quantity you pick. Bulk pricing is the classic case — one yoghurt costs more per gram than the family tub, so heavy users self-select into the cheaper-per-unit deal. Airline cabins, software tiers, the small/large coffee, the annual-versus-monthly subscription: all are self-selection menus. Nobody asks your income; the *choice* you make does the sorting.
Third-degree is the most familiar: split buyers into visible groups and charge each group its own price. Student and senior discounts, weekday-matinee cinema tickets, peak-versus-off-peak trains, regional pricing of the same app — all third-degree. The logic is straight elasticity, the price elasticity of demand you learned earlier: groups whose demand is *price-sensitive* (students, who will skip the film if it costs too much) get the low price; groups whose demand is *insensitive* (the rushed business traveller who must fly today) get charged more. The seller is reading the group's elasticity, then pricing against it.
Third-degree pricing: two groups, one cinema Group Willing to pay Elasticity Price ------------ -------------- ---------------- ----- Students up to $6 price-sensitive $6 Professionals up to $14 price-insensitive $12 The rule behind it (same MR = MC as the monopolist, applied group by group): charge the LOWER price to the MORE elastic group charge the HIGHER price to the LESS elastic group
Marginal revenue is the engine
Why does charging two prices earn more than one? Recall the monopolist's headache from the last guide. A single-price seller who wants to sell one more unit must cut the price for *everyone*, so its marginal revenue sits below the price — every extra sale quietly shaves the takings on all the earlier ones. Price discrimination dodges that tax. By cutting the price *only* for the new, price-sensitive buyer and leaving the high price untouched for everyone else, the seller can chase extra sales without giving up revenue on the buyers who would have paid full freight.
Picture the cinema again. At a single 12-dollar price it sells only to professionals; the seats students would have filled at 6 dollars stay empty, because dropping to 6 for all would gut the revenue from professionals. But if it can fence the two groups apart, it sells at 12 to professionals *and* at 6 to students. Those 6-dollar tickets are pure extra: each one beats an empty seat, whose marginal cost is essentially zero. The seller earns more, and seats that would have gone dark now hold a paying viewer. That second half is the surprising upside we turn to next.
Who really benefits? The honest verdict
It is tempting to file price discrimination under "sellers gouging buyers," and often it does transfer money from your wallet to theirs — the high-paying business traveller is plainly worse off. But the verdict is genuinely mixed, and economists do not all agree on the net effect. The reason is that single-price monopoly is itself wasteful: it sets the price so high that some people who value the good *above* its cost still walk away, a loss to everyone that we named the deadweight loss of monopoly. Discrimination, by reaching those priced-out buyers, can shrink that waste.
Concretely: the student who could never afford a 12-dollar ticket now sees the film for 6; the off-peak traveller flies for 90; cheap generic-region drug pricing lets poorer countries buy medicines priced out of reach at rich-country rates. In each, a trade happens that would not have happened at all under one price. So discrimination can *expand access* and raise total output. That is a real benefit, not seller spin — but be careful: it is not a clean win. The gains are shared lopsidedly, the high-value buyer is squeezed, and whether the world is *better off overall* depends on the exact shapes of demand. It can go either way, which is precisely why honest economists hedge.