I have always found the notion of randomness hard to understand. It is not that I don't understand what people are saying when they use the word "random" in certain everyday contexts, such as when someone says "I was randomly assigned to this team", but that I don't have a clear understanding of how randomness is supposed to be understood as related to probability, chance, and predictability.

Right after the first appearance of the word "random" in his An Introduction to Probability and Inductive Logic, Ian Hacking remarks, "Randomness is a very hard idea." This really struck a chord with me when I first read it. Although Hacking goes on to give something like a definition of "randomness", he is very careful in formulating it:

Outcomes from a chance setup are random (we think) if outcomes are not influenced by the outcomes of previous trials.

Notice the parenthetical "we think".

I am going to read with some colleagues Hacking's famous book The Emergence of Probability. Hope this will help me understand randomness better.


  1. I think that if, for example, a person were to spin a wheel, divided equally into 100 subsections (so that it looked like a pie chart), and the resulting number at the top determined a team placeement, a person might remark, "it was random that I was assigned to Team 2." It is fully apparent, I think, that the probability of being assigned to team 2 was equal to all other outcomes (supposing the case to be an assignment from team 1 to 100), however, there was not a clear causal link between some prior event, and the placement on team 2. The person might look at the wheel and say, "My assignment came without any qualifications for itself, there was no deliberation involved; this is random."

  2. Hi Wai-Hung:

    First of all, I am a friend of Greg Tropea's and am trying to get an update on his health. Please let me know via email (vmehrotra@usfca.edu) if you can, and thanks in advance for your follow up.

    Now, on randomness: I teach probability and statistics (usually to students who have never been exposed to these topics before), and I have found that there is tremendous value in SHOWING probability rather than TELLING people about. I'd be happy to discuss further with you - this is a subject for which I have some passion - and thanks for the tip to Hacking's book...



  3. Randomness confuses me also, especially because there are different kinds of randomness.
    For instance, the numbers produced by a random-number generator are only truly random if they meet specific criteria.
    I don't understand why. This is one of those mathematical problems I'm in the grip of.
    If you find a good book on it, let me know.