For example, I had no idea that probabilities of 0 or 1 don't change with information. I don't recall being taught this in elementary or advanced probability. The advanced probability way of proving it would be with filtrations,

$$P(A|\mathscr F_t) = 1 \iff P(A|\mathscr F_s) =1 \iff P(A)= 1 \iff P(A|\mathscr G)= 1,$$

but there's a way without measure theory to prove a weaker result in elementary probability:

$$P(A|B) = 1 \iff P(A)=1$$

This needs no measure theory!

If I were unsure about the last statement or had no idea about the weaker result and were to ask something like 'How do I/Can I teach the concept that probabilities of 0 or 1 do not change when you add or remove conditions without measure theory?', what tag is or could be (is: it exists, so what is it? / could be: it doesn't exist, so what could be an appropriate tag?) appropriate?

  • 2
    $\begingroup$ I don't think a special tag is needed. Just use some general tags like probability and prerequisites. $\endgroup$
    – JRN
    May 1, 2018 at 10:46
  • $\begingroup$ @JoelReyesNoche i said IS or could be. Prerequisites sounds right. Thanks ^-^ Happy 5th week of Easter $\endgroup$
    – BCLC
    May 1, 2018 at 10:50

1 Answer 1


You can use the tag . For the question in your example, you can also use the tag . Both these tags exist in main. The "prerequisites" tag has the description "The necessary background to learn a certain topic or to follow a course or academic program" and the "probability" tag has the description "For questions about the teaching of probability, dealing with students misconceptions in probability, and explaining probability theory paradoxes."


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