"But Thomas, one of the twelve, called Didymus, was not with them when Jesus came."The other disciples therefore said unto him, We have seen the LORD. But he said unto them, Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe.
"And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you.
"Then saith He to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing.
"And Thomas answered and said unto him, My LORD and my God.
"Jesus saith unto him, Thomas, because thou hast seen Me, thou hast believed: blessed are they that have not seen, and yet have believed."
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As the story of doubting Thomas in the Gospel of John makes quite clear, in the English language the verb "to believe" does not imply believing without evidence. This simple fact is also communicated by the well-known proverb "Seeing is believing", which, as a matter of fact, strongly implies the opposite, and which has been in circulation in the English language at least since the early 17th century (it appears in a collection of proverbs compiled by John Clarke published in 1639, but is even older than that).
The word "believe" appears well over 200 times in the works of Shakespeare, and 18 times in Hamlet alone, where it is first uttered by Horatio in Act One, Scene One:
"Before my God, I might not this believe
Without the sensible and true avouch
Of mine own eyes."
Moreover, the English word "believe" can be used to denote a belief that is based on scientific evidence. Take, for example, this sentence from a January, 2000 NASA press release (link) quoting Yale University researcher David L. Rabinowitz:
"We now believe there are between 500 and 1,000 near-Earth asteroids larger than one kilometer (about 0.6 miles) in diameter."Similar examples are easy to find if one searches the scientific literature for the phrase "we now believe".
At the risk of belaboring this point, let us ask why Rabinowitz says (above) that scientists "now believe there are between 500 and 1,000 near-Earth asteroids" etc., etc.? Is it because these scientists have prayed to their Gods and in answer to their prayers the truth has been revealed unto them? No. (Although it must be allowed parenthetically that a great many working scientists have tried this and will admit to it if they are honest!) Rather, it is because these scientists have examined the evidence and have come to a scientific conclusion based on that evidence.
Moreover, like all scientific conclusions, this conclusion about asteroids contains some (in this case fairly significant) amount of uncertainty. An alternative way of stating "between 500 and 1,000" makes the measure of uncertainty more explicit: "750 plus or minus 250".
Not only do all scientific conclusions involve uncertainty, but all scientific meaurements (aka "data") involve uncertainty. One thing that lay people are often completely ignorant about is the fact that data and uncertainty always go hand in hand, and this even to the extent that any data worth a scientist's attention must include, as an integral part of the data, an estimate (for, quite naturally, there is unavoidable uncertainty when it comes to quantifying uncertainty itself) of the error involved in the data.
To briefly summarize:
1. Belief can be based on evidence, and often is. In fact, the word "belief" often comes up in the context of arguments to the effect that evidence should always be required as a basis for belief.
2. All scientific data, and, necessarily so, all scientific conclusions based upon the analysis and interpretation of data, involve uncertainty.
