[marktani]

edit: totally misunderstood parent, my bad. disregard the following.

> - Take a bag for which “all marbles in this bag are black” is false

> - Add a black marble to that bag

> - After that, “all marbles in the bag are black” becomes true

This reasoning is not correct. If the bag contains exactly a red marble at the start, "all marbles in this bag are black" is false as you required, but it breaks the claim at the end that "all marbles in the bag are black".

There is in fact no bag that fulfills your reasoning, even the empty bag wouldn't (when starting to write my reply I had erroneously assumed so)

[saurik]

If a bag contains exactly one red marble at the start then all marbles in this bag are black is in fact false, but when you throw in a black marble the value does NOT suddenly become true, as the red marble still exists, which is exactly the point of the scenario: adding a black marble to a bag where that claim is false shouldn't make the bag suddenly become true, and it still didn't in your example... it would, though, if the empty bag were defined to be false (which it should not be based on this argument).

[marktani]

thanks, I see my misunderstanding now