Postel’s Law

Jonathan Bruce Postel (1943 - 1998), American computer scientist

Jon Postel helped design the internet. He’s in the Internet Hall of Fame, and he’s best remembered for this:

Postel’s Law

Be liberal in what you accept. Be conservative in what you send.

In other words:

Software programs that receive messages should accept imperfect input as long as the meaning is clear.

Liberal in what they accept.

But programs that send messages to other programs should conform completely to the receiving program’s specs. They should be perfect.

Conservative in what they send.

Postel’s Law was written for software, but it’s bigger than software.

We should expect more from ourselves than we expect from colleagues, clients, friends, and family. And the rest of humanity, while we’re at it. Too often we judge ourselves by our intentions, but others by their actions.

We have that backward.

We should be a light, not a judge. A model, not a critic.

Liberal in what we accept. Conservative in what we send.

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