BHS -> Mr. Stanbrough -> Physics -> About Science -> this page
Suppose you see a beaker filled with a clear liquid sitting on a table in the laboratory. It would be extremely foolhardy, dangerous, and perhaps fatal to "jump to the conclusion" that it was water. There are lots of clear liquids that look like water - and many of them are extremely dangerous. "It is a clear liquid" is an observation, but "It is water" is not ! We could perform physical and chemical tests on the clear liquid from which we might conclude - decide based on observations - that it is water, but the statement "It is water" is a conclusion - not an observation.
The statement "All cows have 4 legs." is NOT an observation, since there is no way that anyone could possibly observe all cows (which must mean all past, all present, and all future cows, by the way...). Perhaps you would call it a fact, but it isn't a fact either (facts are well-confirmed observations). This statement is a conclusion - after observing many cows, a decision has been made concerning the nature of all cows.
It can be tricky to separate conclusions, observations, and facts. A "dead giveaway" though, are words like "all", "every", "none", "always", "never", etc. Any statement containing one (or more) of these words has to be a conclusion. Do you see why?
YES!! - Especially when you "jump to" them!
If "Old Bessie" has an altercation with the tractor and loses a leg (surely this has happened more than once...) she is still a cow - even though she has three legs. The statement "All cows have 4 legs." is almost certainly not strictly true.
What scientists need to do is to try to separate observations from conclusions. This is a difficult job at best! It might not even be possible to completely separate our observations from our preconceived notions and theories, as many philosophers of science have claimed, but scientists seem to succeed, at least to some degree!