Falsification is the action of disproving a proposition, hypothesis, or theorem. It is not falsification but FALSIFIABILITY that is one of the important principles undergirding scientific progress.
Falsifiability — also called refutability and testability — is the logical possibility that a proposition, hypothesis, or theorem can be disproved, either through direct observation (Neil Armstrong "discovered" that the Moon is NOT made of green cheese), logic, or scientific experimentation.
For example, "The sun rises in the East" is a falsifiable statement. "God loves me more than God loves you" is a false statement, but it is not falsifiable. Could you observe that it is not true? Could you rebut it using only the rules of logic? Could you design a scientific experiment to disprove it? (Do you live your life by similar false-but-not-falsifiable ideas, like "God loves me more than God loves Islamic jihadists / Nazi skinheads / gays / abortionists / liberals / left-handed people / women / fill-in-the-blank"?)
Science couldn't be science without the scientific method. A scientist wakes up one morning and wonders about an unanswered question — for example, "Is the sky really a dome made of hammered metal, as the 'inerrant' Bible says it is?" (Gen. 1:6-8, 1:14-17, 7:11, 11:4; Job 37:18; Ezekiel 1:22; Enoch 72:2-5; and many other places)
The next step is to form a hypothesis: "The sky is a dome made of hammered bronze." The scientist will proceed to use observation, logic, or scientific experimentation to see whether or not the sky is made of hammered bronze. (The verses in the Bible that call the sky a metal dome date from the Bronze Age or earlier.) Whether or not it is false, the hypothesis is FALSIFIABLE.
The scientist proceeds to test the hypothesis: will it turn out to be true or false? Then the scientist publishes the results of her tests, and other scientists review the results. Is the scientist's reasoning sound? Are there facts the scientist did not know, overlooked, or ignored? Were the scientist's experiments well designed? Is the data garnered from the experiments reliable? Can the experiments be reproduced by other scientists?
In the next step, many scientists compile dozens and dozens of tested hypotheses to form a theory. Gravity is a famous scientific theory that virtually everyone alive accepts as fact; so are Einstein's theories of relativity.
According to Stephen Hawking (in A Brief History of Time), "a theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations . . . and it must make definite predictions about the results of future observations." The scientific theory of natural selection, commonly miscalled evolution, is a good theory by this definition. The religious hypothesis that evolution is false rejects the literally billions of observations of biology, chemistry, archeology, biochemistry, medicine, and physics, AND all their predictions about the results of future observations, in favor of one theological proclamation that is a MINIMUM of 2,933 years old and must be taken on faith alone.
Hawking adds, "Any physical theory is always provisional, in the sense that it is only a hypothesis; you can never prove it." You can never PROVE that if you jump off the roof, you will fall; gravity might suddenly cease to exist for you, in which case you'd just float there until someone lassoed you down.
"No matter how many times the results of experiments agree with some theory," Hawking continues, "you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation [that] disagrees with the predictions of the theory." In other words, the theory is falsifiable.
Falsifiability is often thought to be the answer to the problems caused by inductive reasoning. For example, "This swan is white" is a statement of observation. "All swans are white" is a statement of inductive reasoning. It was a valid scientific theory for centuries — until someone saw a black swan, that is.
There are two big problems with inductive reasoning. First, there is always the possibility of a black swan. Second, just because something has been true up until now does not mean it must ALWAYS be true. "The sun will rise in the East tomorrow" is a safe bet in the real world, but not in the world of science. There is always the possibility that some time today or tonight, the magnetic poles of the Earth will shift, so that East tomorrow will be where Southeast was today. Or the sun could explode overnight, or the Daleks could kidnap the planet.
Falsifiability attempts to address the problems with inductive reasoning by turning them upside-down. Inductive reasoning says, "If A is true, then B is true. B is true. Therefore A is true." Falsifiability says, "If A is true, then B is true. B is false. Therefore A is false."
But falsifiability is not the be-all and end-all of science, and understanding falsifiability is not the best way to model scientific progress. Falsifiability is like a game of musical chairs, where the one theory left when the music stops must be true. Scientific progress is more like shopping to make stew for dinner when stew hasn't been invented yet. Is the beef too old and stringy? Choose a better package. Are the potatoes gooshy? Are the carrots limp? Hey, I'll bet onions would taste good, let's try some and see. Peas might taste good too, you never know until you try.
Scientific explanations of the world are based not on falsification or falsifiability, but rather on logical thought, carefully designed experimentation, peer review, and reproducibility. Religious explanations of the world are based on faith that the statements in the religion's holy book (a) are immutably True for all time, and (b) no matter how ancient the scrolls of tanned animal skins or mashed river reeds, the holy book was written out of a culture, zeitgeist, and ethos identical to today's. (I have read dozens of arguments about Mary and Martha in the kitchen. In first-century Bethany, there WERE NO kitchens!)
Here is the most accurate model for understanding scientific progress: Moses comes down from the top of the mountain. "God told me to tell you [fill in the blank]," Moses says.
Religious belief says, "Okay, Moses. If you say God said it, then God said it."
Science says, "Sez you, Moses! PROVE IT!"