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No. It's possible that he didn't see anything, of course, but it's also possible that he actually saw the fish, or that he saw something else in the water and was mistaken. If he wants to prove that he saw the fish, then yes, he has to capture a live specimen, but not having one doesn't automatically invalidate his story as a lie. It just means that there's no real reason to believe it.
Unless he can find the fish as proof, then yes. It provides a reason to look into the matter further, but it isn't proof that the fish exists.
No one said it was. It's just that having no proof of it leaves us with no reason to believe it.
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Someone witnessed a glowing fish, something completely unheard of and or 'alien' to them. Certainly no one had ever seen something like this first hand, much less recorded its existence. This lone witness held an accurate report of real creatures.
It would take years for him to be vindicated and were someone to claim they had seen glowing fish, a marine biologist might ask him to describe it, so that he could name it for him.
The REALITY is that these fish have probably existed for billions of years, only in the past 100 has anyone known of their existence. They existed BEFORE science recognized them, but the tip of the explorative sword held the truth the whole time.
We dismissed an account of truth regarding a new discovery, to our detriment.
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*If a King, upon hearing of an approaching army, sent out a scout to bare witness to this invading army and what types of armaments they planned to employ, AND to take pictures.
The scout witnesses that the invaders have only a series of catapults, no calvary, archers, and only a few infantry men. Sadly all the pictures were lost, over-developed, rendered useless. The King has to develop a defense strategy and looks to his war counsel. The 'skeptics' argue that the scout COULD be wrong, that maybe he just didn't 'see' the calvary and archers, and that ANY defense plan should ignore any report of catapults without pictures of them. The scout himself argues that a small team of demolition assassins should be sent out to destroy the looming artillery...
Should the King take the word of a single man, or should the skeptical argument win the day? Should he send out a small demolition team, or empty out his own calvary and archers to make a full defense?
There is a war on, and every unit is invaluable...
'I' heed my scout's report.
Be as skeptical as you'd like. It won't deliver you timely truth.