Probability
Probability assigns a number between 0 and 1 to an event, with 0 meaning impossible and 1 meaning certain. Since 1933 the standard treatment has been Kolmogorov's: outcomes form a set, events are subsets of it, and probability is a function on those subsets that is never negative, gives the whole set the value 1, and adds up over events that cannot occur together. The mathematics is settled; what those numbers mean is not, and interpretations divide roughly between long-run frequency and degree of belief.
Why it matters
It is the branch of mathematics most used outside mathematics, and the split between its two interpretations is behind most arguments about statistics.
Also written: probabilities, chance
Where it comes up
Read about Probability on Wikipedia
Sources
- Probability Wikipedia
- Interpretations of Probability Stanford Encyclopedia of PhilosophyLays out the frequency and degree-of-belief readings and what each one gets wrong.
