Probability as Physical Propensity/Tendency
- under this view, probabilities are generated from direct physical observation and maybe from analyzing the physical properties of the objects involved in the process
- for example:
- a coin lands heads or tails with a propensity of 0.5 (this isn’t quite true because regular coins do land on their edge once in a few thousand flips)
- a fair die has a propensity of 1/6 to land with either side facing up
Reliance on “The Law of Large Numbers”
This definition of probability is somewhat complementary to the frequentist one. It specifies the source of the long-term frequency of occurrence of certain events. Namely, the physical properties of the objects involved in the process.
For that, it relies on the law of large numbers.
Relation to Other Definitions
- The advantage this definition has over the frequentist one is that here you can talk about probabilities of single events and not just long-term frequencies.
- The propensity definition also explains the principle of indifference to the physical properties of objects. For example, a die is not biased to land on any particular side precisely because it is a perfectly symmetric cube, has a uniformly distributed density, and so on (of course, no real die is really that perfect).