ok how do you verify this statement: "all swans are white"
when
you make a positive claim
the BURDEN OF PROOF lies on
you
and any claim that does not have empirically verifiable evidence and or is not demonstrated to be logically necessary
has no detectable "truth value"
and is relegated to
OPINION
i see you had no answer to that, so allow me explain
first of all, it's of no significance whether the claim is "positive" or not. You can convert the statement to a negative one; the contrapositive, logically equivalent "there is no swan that is black"
i would recommend expanding the vocabulary beyond "fact" and "opinion", because these terms are meaningsless from an epistemological point of view
the point that you're missing is that the 2 statements
- "aliens exist"
- "all swans are white"
are epsitemologically different; the first one is verifiable but not falsifiable. As such, as far as arriving at concrete answers is of concern, it's actually somewhat pointless to debate that statement (and which is why it's subject to "belief" and endless discussion, where people talk about "evidence"). The second one is not verifiable but it's falsifiable; observing more white swans corroborates the conjecture, but it doesn't verify it. Whereas if you observe a black swan, you have falsified it and can safely say that the statement is false. Which is why falsifiable statements are those that are scientifically useful