How Voting Systems Shape Outcomes

To keep this politically neutral, every example below uses fictional parties (Blue, Green, Yellow) and fictional candidates (A, B, C) — the point is the mathematics of vote-counting systems, not any real party, country, or election.

Demonstration 1: Same national votes, different seats

Set how the country votes nationally, then compare two real counting systems: First-Past-The-Post (FPTP) — 20 separate local districts, each awarding its one seat to whichever party gets the most votes in that district — versus Proportional Representation (PR) — 20 national seats handed out to match each party's overall vote share directly.

Proportional systems mirror the vote. Winner-take-all district systems mirror where the vote is, which is a different thing entirely.

Notice what happens at "even everywhere" (support identical in every district): the national leader can sweep every single seat under FPTP despite winning well under half the national vote — because winning a district by one vote is worth exactly as much as winning it by a landslide, and every district happens to break the same way. As support becomes more geographically varied, FPTP results drift closer to (though rarely exactly matching) the proportional split, because different regions start favoring different parties. This single mechanical fact — not corruption, not conspiracy — is why the same country, and the same votes, can produce a governing majority under one counting system and a coalition parliament under another.

Demonstration 2: Vote-splitting and the "spoiler" effect

Now a single-seat race: Candidates A, B, and C, with C running third. Suppose B and C appeal to similar voters. Under simple plurality (most votes wins, one round), whoever has the most first-choice votes wins outright — even without a majority. Under ranked-choice / instant-runoff voting (IRV), the last-place candidate is eliminated and their voters' next choice is redistributed, repeating until someone has a majority.

At high similarity (C's voters mostly transfer to B), the IRV winner can flip to B — someone who wasn't ahead in round one, but who a clear majority preferred once the race narrowed to two. At low similarity, the plurality leader (A) holds on either way. This is the mathematics behind the real, well-documented "spoiler effect": under plurality voting, a similar third candidate can split a bloc of like-minded voters and hand the race to someone most voters, given the final choice, would not have picked. IRV is one attempt — among several — to fix exactly this mechanical problem, with its own different trade-offs.

Why none of these systems is simply "the correct one"

Each system optimizes for something real and defensible, at a genuine cost to something else:

FPTP gives every district a clear, local, individually accountable representative and tends to produce decisive single-party governments — at the cost of potentially large gaps between national vote share and national seat share. PR makes the legislature closely mirror how the whole country actually voted — at the cost of weaker single-district accountability and, often, coalition governments that require post-election negotiation. IRV reduces spoiler effects and vote-splitting — at the cost of a more complex ballot and count that some voters and officials find less immediately intuitive than "most votes wins." Countries make genuinely different, defensible choices here, and many use different systems for different offices within the same country.