I have seen random and unpredictable used interchangeably but sense there is a subtle difference that I have difficulty articulating. My sense is that predictability is based on my own personal experience while random behavior doesnt need any of my personal experience. Any help is greatly appreciated.

  • 1
    Both randomness and predictability are based on available knowledge ("personal experience"), that is not the essential difference between them. The difference is that random processes follow a probability distribution, and hence, in some respects, are quite predictable. Think of a sequence produced by tossing a fair coin. It is random, but has, on average, equal numbers of heads and tails. What some mathematicians call lawless sequences do not have to display even such regularity, unpredictable goes beyond random.
    – Conifold
    Jan 23, 2023 at 10:47
  • @Conifold It seems that a main component to unpredictability is ignorance. Something that has a pattern that I am ignorant of is unpredictable to me. A random process does not have this restriction
    – user64314
    Jan 23, 2023 at 15:20
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    Randomness has the same restriction, the reason you are assigning probabilities to outcomes is, typically, that you are ignorant of something about the process producing them. If you knew precise conditions of tossing a coin and had unlimited computational resources you could, in principle, predict the outcome.
    – Conifold
    Jan 23, 2023 at 18:40
  • @Conifold Isn't there a control aspect to this? Through the acquisition of knowledge I have a chance to "convert" a process from unpredictable to predictable. Does the acquisition of knowledge change a random process to a non random process?
    – user64314
    Jan 23, 2023 at 18:50
  • Chaos is deterministic but unpredictable. en.wikipedia.org/wiki/Chaos_theory
    – user4894
    Jan 23, 2023 at 21:22

3 Answers 3


Randomness is a complicated concept with different meanings in different contexts. Unpredictability is common to all meanings of random, but everything unpredictable is not random.

In statistics, randomness means lack of pattern, unpredictability of the next item in a series.

In physics, randomness refers to the probabilistic variation, inaccuracy in all events. Causes never determine their effects with absolute accuracy, there is always a random, unpredictable component yielding slightly different effects for similar causes.

In philosophy and in common speech, random means unintentional, accidental, not planned, serving no purpose, aiming at no goal. The opposite of random in this sense is naturally intentional, planned, done for a purpose, aiming at a goal.


No they are not equivalent. Unpredictability has a wider meaning than randomness. Random means that there is no systematic pattern. Unpredictable can mean that there is a pattern but you do not know what it is.


Unpredictable means it is impossible to predict. Random means it can be predicable or unpredicatble but you dont know between this two determined features.

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