Plural mechanisms: quadratic voting, funding & Harberger taxes

A plain vote captures direction (yes or no) but not intensity — it can’t tell the person who barely cares from the person whose life depends on the outcome. The RadicalxChange movement (sparked by Glen Weyl and Eric Posner’s 2018 book Radical Markets) designs mechanisms that fix this by borrowing the logic of markets and putting it to democratic ends. These are tools for the plurality toolkit, not a single fix.

Quadratic voting

You get a budget of “voice credits” to spend across many issues. The twist: votes cost the square of how many you cast — one vote costs one credit, two votes cost four, three cost nine. So you can express that you care intensely about one thing, but it costs you dearly everywhere else. This makes people weigh honestly how much they care, instead of yelling “maximum” on everything. In effect, each voter pays for the cost they impose on others by being louder. It’s a way to give democracy higher bandwidth — more information per person than a tick-box every few years. (The square-root math has a neat origin: it’s how uncorrelated voices average out as noise while one correlated voice stands out — so the mechanism deliberately lets a shared voice be heard without letting it dominate.)

Quadratic funding

Apply the same idea to money for public goods: donations act as votes, and a matching pool amplifies projects backed by many small contributors over those backed by a few large ones. A project that 100 people each give £1 to can beat one that a single donor gives £100 to — the breadth of support counts, not just the size. Quadratic-funding rounds have distributed many millions of dollars to public goods this way, and Taiwan’s presidential hackathon uses quadratic voting to pick which civic projects get backed.

Harberger taxes & SALSA (sharing property)

The third idea rethinks ownership itself, building on the 19th-century economist Henry George’s insight that most of a plot’s value comes from the community around it, not its owner — an empty Manhattan would be nearly worthless. Under SALSA (Self-Assessed License Sold at Auction, also called a Harberger tax or partial common ownership) you self-declare what your possession is worth, pay a fee on that figure, and must sell at that price to anyone who offers it. Lowball the value and someone buys it cheaply; overstate it and you pay more — so you’re nudged toward honesty. The fees flow back to the community that creates the value. It reframes ownership as stewardship on behalf of a community rather than absolute dominion — the market-mechanism cousin of relational property.

Handle with care

These tools are powerful but, as a 2024 Plurality in Practice study found, easy to mis-calibrate. Bridging-weighted (“connection-oriented”) voting needs good data about who is grouped with whom; with missing data it quietly collapses back to ordinary quadratic voting. And the “magic” happens in opaque back-end math — even Polis makes many hidden modelling choices — so few implementers ever adjust the defaults. The honest takeaway: match the mechanism to the context, and don’t mistake novelty for proof that the design itself is what worked.

Sources

• “Collective Decision Making with Matt Prewitt” — Green Pill #25 (2022): youtube.com/watch?v=9UYjLiKvx68.
• “Salon IV: Plurality in Practice” — Protocol Symposium (2024): youtube.com/watch?v=snnk_8q1w_4.
• Eric A. Posner & E. Glen Weyl, Radical Markets: Uprooting Capitalism and Democracy for a Just Society (Princeton, 2018).
• Plurality: The Future of Collaborative Technology and Democracy: plurality.net.