The term scientific method refers in general to the procedures that scientists follow in obtaining true statements about the natural world. As it happens, scientists actually use all manner of procedures to obtain the information they want. Some of those procedures are not very objective, not very formal, and not very systematic. Still, the "ground rules" by which science tends to operate are distinctive and very different from those by which "true statements" are produced in philosophy, the arts, history, ethics, and other fields of human endeavor.
Many science textbooks begin with an exposition of a system of thought that, at least in the ideal, describes the way scientists work. The system is actually a cyclical process, one in which it is impossible to say where the whole process begins.
Certainly one element in the process is the recognition of a problem or the desire to know something specific about the natural world. For example, one might wonder whether an airplane flies better with narrow wings or broad wings. In most cases, a scientist poses a question such as this in terms of a hypothesis. A hypothesis is an idea phrased in the form of a statement that can be tested by observation and/or experimentation. In this example, the hypothesis might be: "Airplanes with broad wings fly better than airplanes with narrow wings."
The next step in the procedure is to devise ways of testing that hypothesis. In some cases, one can simply go out into the real world and collect observations that will confirm or deny the hypothesis. In most cases, however, a scientist will design one or more experiments to test the hypothesis. An experiment is really nothing more than a set of procedures designed to test a given hypothesis. Experiments are generally more productive than observations in the natural world because they deal with only one specific aspect of the whole world. Confusing factors can be intentionally omitted in order to concentrate on the one factor in which the scientist is interested.
In the case of airplane wings, one approach would be to design a series of airplanes, each with wings somewhat broader than the others. Each plane could be flown, and the efficiency of its flight noted.
Experiment: A controlled observation.
Fact: A statement that is widely accepted as being true by scientists.
Hypothesis: An idea phrased in the form of a statement that can be tested by observation and/or experiment.
Scientific law: A statement that brings together and shows the relationship of many scientific facts.
Scientific theory: A statement that brings together and shows the relationship of many scientific laws; also, but less commonly, another term for hypothesis.
The results of observations and/or experiments permit scientists to draw conclusions about the hypothesis. In our example, a scientist might discover that airplanes with broad wings fly better or not as well as airplanes with narrow wings. Or the results of experimentation may indicate that flying efficiency seems unconnected to wing width.
Imagine that a scientist, however, discovers that every broad-winged airplane flies better than every narrow-winged plane tested. Can it then be said that the original hypothesis has been confirmed?
Probably not. One critical aspect of science is that no hypothesis is regarded as true until it has been tested and re-tested many times. If two dozen scientists all perform the same experiment and get the same result, then confidence in the truth of that result grows. After a long period of testing, a hypothesis may begin to take on the form of a fact. A fact is a statement that is widely accepted as being true by scientists.
Interestingly enough, it is never possible in science to prove a statement true for all time. The best one can hope for is that a fact is not proved wrong. That is, maybe the one-hundred-first time a fact/hypothesis is tested, it is found to be incorrect. That single instance does not necessarily prove the fact/hypothesis wrong, but it does raise questions. If additional "false" results are obtained, the hypothesis is likely to be rejected as "not true."
The cycle of the scientific method is completed when a new fact has been learned. In most cases, that new fact will suggest new questions, new hypotheses in the minds of scientists. For example, if broad-winged airplanes do fly more efficiently than narrow-wing airplanes, then what is the effect of making the wings fatter or thinner? As soon as that question (or one like it) occurs to someone, the cycle of hypothesizing, testing, and concluding begins all over again.
Obviously, untold numbers of facts exist in science. The process of learning a new science is, to a large extent, learning the facts that make up that science.
But individual facts in and of themselves are not very useful in science. Their greater importance lies in the variety of ways in which they can be combined to make more general statements about nature. For example, it might be possible to make a factual statement about the boiling point of ethyl alcohol, a second factual statement about the boiling point of propyl alcohol, a third factual statement about the boiling point of butyl alcohol, and so on. But what is of greater interest to scientists is some general statement about the boiling points of all alcohols in general. General statements that bring together many, many related facts are known as scientific laws.
Scientific laws, like individual facts, often suggest new questions, new hypotheses, new experiments, and, eventually, new facts. These facts tend to make scientists more confident about the truth of a law or, in some cases, raise questions as to the law's correctness.
One more step of generalization exists in science: scientific theories. A great deal of confusion centers on the word "theory" in science. Most people use the word theory to suggest a guess about something: "I have a theory as to who stole that money." Scientists sometimes use the word in the same sense.
But theory can mean something quite different in science. A scientific theory is a system of generalization even larger and more comprehensive than a scientific law. Just as a law is a collection of facts, so a scientific theory is a collection of scientific laws.
This definition explains the misunderstanding that some nonscientists have about the use of the word theory. Some people may believe that the theory of evolution is only a guess, as the term is used in everyday life. But the word theory is not used in that sense here. The theory of evolution refers to a massive system that brings together many, many laws that describe the way organisms change over time. Biologists are not guessing that these laws are true; they are supremely confident that they are, in fact, true.
The scientific method has been a powerful tool for learning a great deal about the physical world, but it is not a system for answering all questions. The only questions science can attack are those that can be answered by using the five human senses in one way or another. For example, suppose that someone hypothesizes that the reason earthquakes occur is that tiny invisible demons living under Earth's surface cause those events. That hypothesis is, by definition, untestable by scientific methods. If the demons are invisible, there is no way for scientists to observe them. One might look for indirect evidence of the demons' existence, but the problem is probably beyond scientific investigation.
It is for this reason that topics such as love, hope, courage, ambition, patriotism, and other emotions and feelings are probably beyond the scope of scientific research. That statement does not mean these topics are not worth studying—just that the scientific method is not likely to produce useful results.
Another question that the scientific method cannot solve is "why?" That statement may startle readers because most people think that explaining why things happen is at the core of scientific research.
But saying why something happens suggests that we know what is in the mind of someone or something that makes events occur as they do. A long time ago, scientists decided that such questions could not be part of the scientific enterprise. We can describe how the Sun rises, how objects fall, how baseballs travel through the air, and so on. But science will never be able to explain why these things occur as they do.