Hello, I’m Pang Ying.

Have you heard this argument? If same-sex marriage becomes legal, must pedophilia follow, then marriage to monkeys or tables? That is absurd, so same-sex marriage must remain illegal.

This familiar pattern is the slippery-slope argument, today’s subject.

A slippery slope is often a logical fallacy.

It says A will cause B, B cause C, and so on until Z. Because Z sounds terrifying, A must be prohibited.

Why is that fallacious?It never proves that each link holds. Unsupported step follows unsupported step until an alarming conclusion is asserted.

Consider several examples.

Use a colleague’s pen without asking today, their wallet tomorrow, then everyone’s wallets, and you become a thief. Therefore never touch the pen.

Legalize voluntary euthanasia and soon involuntary euthanasia will follow, then extermination of supposedly inferior people and fascism. Therefore euthanasia cannot be legal.

Restrict American gun ownership and complete prohibition follows; citizens then cannot resist terrorists, who take control. Regulation therefore causes America’s fall.

If seventy-one miles per hour is no different from a seventy-mile limit, neither is seventy-two from seventy-one, until anyone driving seventy-one will drive 130.

Why do these sound unreasonable?No causal step is necessary; some are weak and others absurd. One event does not automatically produce the next.

A car rolling ten meters downhill need not slide to the bottom. We can brake, turn, or meet an obstacle. A does not guarantee Z, so Z’s horror alone cannot prohibit A.

Borrowing a pen and taking a wallet have different moral characters. A moral boundary blocks the slope.

Quantitative accumulation can also cross qualitative thresholds. Accepting a five-percent tolerance around seventy does not mean accepting unlimited speed.