> Filter isn't the existence of other civilizations, but over the probability mass they'll cross paths with another and each can mutually grok the other exists

> Filter isn't the existence of other civilizations, but over the probability mass they'll cross paths with another and each can mutually grok the other exists The idea is that "probability mass they'll cross paths with another and each can mutually grok the other exists" is a monotonically increasing function of the number of other civilizations, which bridges the problem you've identified.