Was talking with someone about the existence of aliens and how I felt like it was a certainty that they existed elsewhere, which made me wonder if I could logically "prove" that sentient life exists elsewhere. This led to the following "thought exercise":
Accept the assumption that we can consider ourselves sentient beings for the sake of this argument. We can conclusively say that sentient life exists here on this planet. Putting the semantics of whether or not we “exist†at all – we are here, and therefore sentient life exists here on this planet.
That fact is the basis for a second fact: at any place other than here, it can conclusively be said that sentient life exists elsewhere. Elsewhere is not defined, and because we have not limited “where†sentient life is other than to “elsewhereâ€, we can assert that sentient life exists anywhere except where we have proven it does not.
Assuming that our second point of reference is devoid of sentient life, that point is one that can be safely excluded from our assertion. We have now assumed, for sake of fairness, but cannot prove, that one point in space is devoid of sentient life, and that sentient life exists everywhere else that we cannot conclusively prove it does not.
Are there any obvious failures in this assertion that make it moot, or did I just manage to logically justify a positive assertion about existence of life elsewhere in the universe? (Or did I just reassert something someone else already said?)