# Propensity vs. Probability

What is the semantic difference between propensity and probability?

I'm thinking of a context like "Given his habbits, he has a high probability of dying of cancer".

Would the choice between propensity and probability be entirely taste-based here? Are there cases where they cannot be used synonymous.

• I've put in an answer, but do note you can just glance in a dictionary for this one! – Fattie Feb 27 at 15:49
• I have a probability for mischief... – Jim Feb 27 at 21:55
• Thanks. As mentioned in a comment to you answer. The reason that I did not trust the dictionary is that in some fields propensity is used seemingly in ways that are more closely related to probability. But I see that these are technical terms (propensity probability, propensity score) – sheß Feb 28 at 10:24

They're totally, utterly, different and totally unrelated.

A "propensity" is a quality of a person.

For example, I have a propensity to drink too much, I have a propensity to post on the ELU site, I have a propensity to get drunk (mentioned that one!), you have a propensity to watch sci-fi movies, etc etc.

"Probability" is a mathematical term and is just totally unrelated.

It has nothing at all to do with describing a person's propensities.

So, the probability of tossing heads is 50%, smokers have a 73% probability of cancer, I have a 88% probability of liver damage, etc etc.

"Propensity" is a quality of a person - simply, it relates to their choices in life.

(Your particular example perhaps leads to confusion, because, the sentence happens to include "a person" in the sentence. But notice it is totally unrelated to their propensities - i.e., "things they like to do / usually choose". You're just stating a mathematical probability. "Research shows that for his habits, he has a 82% probability of contracting cancer.")

• I think what got me confused is stuff like propensity probability, propensity score, where propensity clearly used in a sense that is not related to people. But then again these are technical terms... – sheß Feb 28 at 10:22