How we change what others think, feel, believe and do
A big problem in science and social research is the question of proving whether a statement is true or not, where truth is defined as common agreement about the validity of the statement. We all have our individual truths, but only when target people agrees a truth does it have any external value.
The simplest way of creating truth is simply to assert a belief to be true, and this is regularly used even by scientists today. Various means are used to strengthen the assertion.
Assignment to unquestionable source
In science, the assignment is typically to the current paradigm, whether it is Newtonian Physics, Quantum Mechanics or whatever. It may also be assigned to a canonized text or theorist.
The religious equivalent is to assign truth to God, either as written in the Bible (the Koran, etc.) or to the Priests who are mouthpieces of God.
Common sense and other forms of coercion
The other common use of assertion is to state something as 'common sense', with the implication that anyone who challenges the statement does not have common sense and hence is too stupid to challenge it anyway.
Other forms of coercion includes the physicality with which a statement is made (eg. loud voice, staring, etc.) and various persuasive methods as found elsewhere in this website!
The Rationalist approach is to use logic and structured argumentation to prove a point. Note that as it is internal, a rational truth, although it is more believable, may still be considered to be a belief.
Agreement, not coercion
To make a rational argument, all players must be allowed to make assertions, but others must also be allowed to challenge them. Because no external proof is needed in logic, the only conclusions of an argument can be that people agree or they disagree. Truth is thus still an internal construction and comes from agreement rather than the coercive approach of assertion.
Rational arguments often use conditional statements, of the form 'if A then B', and seeks to gain agreement on types of belief. The logic applied typically makes significant use of mathematical set theory and Boolean Algebra.
Verification (also known as Confirmation or Justification) is an approach used within science for many years for proving that hypotheses are true. It was used for a long time in Positivism.
Verification assumes that an assertion of A=B need only be shown to be true once (or a few times) to be forever true.
Proper verification requires observable, empirical evidence. Rather than argue that something is true, verification shows that it is true. This is based on the assumption that when several people observe something, they perceive the same thing and can draw similar conclusions and meanings about it.
The classic method of verification is to set up an experiment that includes both a control and a target group, and through controlled conditions showing that the target group exhibits the hypothesized behavior solely because of an extra stimulus or different condition that they were given that the control group were not.
The problem with verification, as Karl Popper pointed out, was that just because you can show something to be true in one set of circumstances, you cannot then use induction to create a general truth that is true in all circumstances.
Falsification assumes that an assertion of A=B is true only if all possibilities of A<>B are shown to be false (which is often a much larger domain).
Start from anywhere
Whereas a verificationist inductive approach starts with observation and then forms a theory to test elsewhere, falsification allows you to start anywhere, with any theory or assertion you like. The reason for this is that silly statements are easily falsified.
Testing for falsehood
The basic principle of falsification is that truth is created when falsification efforts fail. The idea is thus tested with the intent of proving it false, thus deliberately overcoming the trap of confirmation bias.
The problem so far with falsification is that you could start with an assertion that Elvis has reincarnated on Venus, and because you cannot prove it false you might assume that it is true. Falsification thus includes the condition that reasonable tests can be done - in this case traveling to Venus and searching every nook and cranny (and then doing DNA tests on the glittering creatures found there).
And the big