Lesson 1 - Likelihood

[kwcflynn]

I am referring to page 1-5 of the coursebook and reviewing my notes for Likelihood. I understand that Certainty is strictly 100% because we know it will happen (or will not happen) and that Probability ranges 51% - 100% because it entails that it's more likely that it will happen. I have been receiving mixed pieces of information on whether or not Probability is "inclusive of certainty." It was mentioned that we can move down the "Likelihood Ladder" (Certainty -> Probability -> Possibility), but we can never move up. However, it was also noted in my lesson that Probability IS "inclusive of certainty.

HELP PLEASE

[Dave Killoran]

Hi K,

Thanks for the question! The key point here is that you can never move up the chain with absolute conviction, but you can go down with conviction (I'm avoiding using the word certainty here since it's in the terms). As in, it's possible to go up, but not known for sure that you can. Let's use an example:

• Certainty -> Probability -> Possibility
  
  Let's say it known that is certain there will be a lunar eclipse this Saturday. From that, I can deduce that it is also probable, as well as that it is also possible. Certain automatically implies those two.
  
  On the other hand, let's say it is just known that it is possible there will be a lunar eclipse this Saturday. That means it may be probable, and it may even be certain (if we get other info), but I don't know for sure that it is is probable or certain.

This difference between known for sure and not known (depending on the direction you are going) is what is causing the issue you described, so the key is understanding what you are trying to infer from each term. You can go "down" towards the less certain term for sure, but you can only go "up" to the more certain term under the chance it can occur.

And, to directly answer your question, Possible includes the chance that Probable and Certain occur; Probable includes the chance that Certain occurs. This is similar to how Some includes the possibility that Most and All occur, and Most includes the possibility that All occurs. When you go "up" the chain toward a positive absolute (Certain/All/etc) possibilities are what you get. When you reverse it, then you can make more solid inferences (Certain automatically means Probable and Possible, and Probable automatically means Possible; All automatically means Most and Some, and Most automatically means Some).

Please let me know if that helps. Thanks!