On the question of what constitutes evidence, I'm inclined to agree what Yazata posted above. A reasonable starting point is that something is evidence for something else if it tends to make that "something else" a more reasonable conclusion that it would otherwise have been. That is, evidence is supposed to provide a
rational justification for a belief or conclusion.
The general question of the circumstances under which we can say we know that something is the case is the subject of a whole branch of philosophy, namely epistemology. Evidence is a tricky thing to get a proper philosophical handle on.
As has been demonstrated in this thread, another question which frequently arises is the quality of purported evidence for a conclusion. In that regard, I agree with Ophiolite's annoyance number 2, in which he points out that saying it would be nice if more people took care to replace "There is no evidence for X" by more accurate expressions such as "There is no
good evidence for X" or "There is no
convincing evidence for X" or "The purported evidence for X does not unequivocally compel us to accept X, and have you considered Y or Z instead?"
Taking the UFO example as a case in point, the problem is clearly not lack of evidence. Magical Realist can provide us with endless poorly-shot videos and breathless "eyewitness accounts" of alien encounters. This is all evidence of a sort. But evidence of what? As Bells pointed out, the UFOlogists tend to start with piece-of-evidence A and then jump to conclusion E, while completely skipping the necessary steps B,C and D that require a sober evaluation of the strength of the evidence, its provenance, and other possible conclusions consistent with the evidence. This is not restricted to UFOs; it applies to virtually
every kind of pseudoscience and, more generally, pseudo-scholarship.
Pseudoscientists - at least the ones who aren't knowing frauds - are generally not educated in either critical thinking or in the scientific method. Therefore, they tend to be very poor at evaluating the quality of evidence. Science - unlike pseudoscience - is far more likely to subject claims to rigorous scrutiny. New claims in science are usually met with a healthy skepticism by the professionals in the field. Scientists are always on the lookout for errors in the work of other scientists, and in their own work, because if they don't weed out their own errors in thinking or evaluation then others will likely do it for them, sooner or later. Confirmation bias is always something to look out for. In pseudoscientific fields, confirmation bias is king. The UFOlogist
wants so much to see alien spaceships that he will often go out of his way to ignore everything that
doesn't scream alien spaceship! to him.
Let's finish by looking at Magical Realist's summary of the evidence for alien spacecraft:
"The evidence is for intelligently operated craft that are beyond the technological capability of humans, that elude jet pursuit, that register on radar, that emit huge amounts of energy, that rarely make any sound, that have physical effects on vegetation, automobiles, and eyewitnesses, and that have been witnessed with occupants exiting them. While their identity remains in question, their existence is well confirmed by the evidence."
I have some questions:
Is there any actual evidence that any UFOs are "intelligently operated craft" controlled by non-human operators?
How are claims of behaviours "beyond the technological capability of humans" tested by UFOlogists? It isn't enough to just watch an object in the sky and conclude that it is moving at hypersonic speed in ways that are technologically impossible. You have to know, for example, how far away the object is, how big it actually is, correctly identify it it the first place, and so on and so forth. You also need a good working knowledge of the technological capability of humans.
Jets have been known to pursue the planet Venus. It's strange that no matter how fast they fly, they never quite manage to catch up with it. Or maybe not so strange.
Lots of things register on radar, like rain clouds for example. What makes a particular radar blip unequivocally an alien spaceship?
How do UFOlogists
measure the "huge amounts of energy" emitted by UFOs? In what form is this energy emitted?
Lots of things rarely make sound. High-flying jet aircraft often can't be heard from the ground, for example. Have all other soundless mundane objects been ruled out as possibilities?
Similarly, lots of things can have physical effects on vegetation, like last time I ate some cereal. Likewise cars.
Then there are all these "eyewitnesses" to close encounters with actual alien beings. How do we know these people are trustworthy? What if it turns out that some of them have been exposed as untrustworthy? Does that mean we can still trust all the rest until/unless they too are exposed? Do eyewitnesses ever make mistakes? Do people ever have dreams or hallucinations that seem real to them? I wonder.
