Question 1

What is the difference between Parkinson's law and Hofstadter's law?

Accepted Answer

Two mock-laws about time that fail in opposite directions. Parkinson's law (The Economist, 1955) says work expands to fill the time available, so a generous deadline gets used up. Hofstadter's law (Gödel, Escher, Bach, 1979) says 'it always takes longer than you expect, even when you take into account Hofstadter's law', so a tight estimate gets blown. One warns against giving a task too much time; the other against trusting your guess at how much it needs.

Question 2

How do I know if I mean Parkinson's Law rather than Hofstadter's law?

Accepted Answer

Readers who land here meaning Parkinson's Law rather than Hofstadter's law are usually searching for phrases like “what is parkinsons law”, “does work expand to fill time”, “parkinsons law explained”.

Aspect	Parkinson's law	Hofstadter's law
Claim	Work expands to fill the time available	Things take longer than you expect
Author and date	C. Northcote Parkinson, 1955	Douglas Hofstadter, 1979
Failure mode	Too much time, quietly used up	Too little time, overrun
The twist	Satire aimed at bureaucracy	Self-referential: allowing for it doesn't help

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Parkinson's Law

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