There is just one small problem with the subjective theory of value. We are assuming wants and desires to be relatively constant. What if they could be manipulated? Would that mess with our conception of value? Do you believe in the existence of dark, arcane forces that conjure up cravings and desires for goods and services that we, the consumer, have literally zero use for? Let’s talk about marketing. Because with marketing we can meddle with desires and manipulate demand.

The diamond industry understands this well, and this is what nets us cute romantic tales about the origin of diamond engagement rings: Consider De Beers, a South African diamond cartel that has historically controlled up to 90% of the global trade of rough diamonds. From the get-go, their advertisers understood that they were trying to market a product with very little use value:

"We are dealing with a problem in mass psychology. We seek to ... strengthen the tradition of the diamond engagement ring -- to make it a psychological necessity (5) capable of competing successfully at the retail level with utility goods and services...."

De Beers (6) bombarded the American and global public with marketing campaigns from the late 1930s onward. They organised lectures at high schools to preach the importance of commitment and diamonds’ association therewith. Celebrities were given diamonds to use as “symbols of indestructible love”. The slogan “A Diamond is Forever”, commissioned in 1947, probably inspired the James Bond book, film and song of the same name. De Beers succeeded in cementing the idea that love, romance, commitment, and seduction can be bought with a 1.4-carat De Beers™ Diamond Engagement Ring.

What’s more impressive is that this alteration of culture and social scripts was not a one-time heist but is a still-ongoing process. The behemoth’s meaty marketing fingers have been massaging our socio-cultural norms for almost an entire century now. A necessary process to keep demand constant despite ever-changing supply conditions:

In the mid ’60s (7), new diamond mines were discovered in Siberia. De Beers feared that the small diamonds mined there would undercut the prices of larger diamonds mined by De Beers in Africa. Quickly a deal was struck with the Soviets to control the new influx of diamonds. The new mines joined the cartel which meant that the smaller Siberian gemstones were now De Beers’ responsibility.

Up to that point, De Beers had popularised a clear message: The bigger the diamond, the better. Previous campaigns had equated larger-sized diamonds with more love and more commitment. A complete 180 on this message was necessary. The advertisers were instructed to highlight the importance of a diamond's cut, colour and clarity rather than its size. It had to be clear that even a small diamond bears emotional significance. The campaigns were a success. The average size of diamonds sold fell considerably until it reached .28 of a carat in 1976 - roughly the average size of the Soviet diamonds.

If anything, the manipulation of public perception had gone a little too well. At times, the demand for small diamonds outpaced supply, forcing De Beers to backpedal a bit and nudge demand in the direction of larger diamonds, like in this ad: