All humans live with beliefs, and they aren't just limited to an individual's political or religious views. Rather, these also include any propositions that an individual has judged to be factual and therefore doesn't doubt. For example, I believe that exercising is good for my health, so I don't need to question every single second while doing exercise whether it is worth my time. I believe that I won't die in the next few seconds, so I don't have to live in a constant state of existential dread. As such, regardless of whether something is "objectively" or "actually" true, beliefs eliminates the need for doubt and constant dissatisfaction; it guides our behaviors in a habitual and automatic way.

Then, how do we come to such beliefs? According to the pragmatist philosopher Charles Sanders Peirce, doubts are what stimulates inquiry, which in turn leads to the settlement of opinion. In his book "The Fixation of Belief," Peirce introduces four methods of inquiry: 1) method of tenacity, 2) method of authority, 3) a priori method, and 4) method of science.

Method of Tenacity

The first and easiest method of inquiry is the method of tenacity. This method eliminates doubt by dismissing its causes. Any evidence that conflicts with a belief is simply shut out. Although it might sound only applicable to zealots, method of tenacity is surprisingly common as it is a human tendency to dislike an undecided state and be comfortable. However, it also makes the developed belief extremely hard to maintain, as we live in a world where things often go against our will. Thus, method of tenacity comes into effect only when the inconvenience caused by holding onto the belief preferable to the irritation caused by doubt. Additionally, humans are social animals. For an individual to live in a society, and for a society to function as a whole, method of tenacity is futile.

Method of Authority

On the other hand, the method of authority addresses such issues. Through indoctrination from an external force, individuals are compelled to fix their beliefs. Common examples include governments, religious institutions, media corporations, sociocultural traditions, and even parents. By using a mix of direct methods like law enforcement and indirect methods like discouraging free expression, method of authority is an extremely effective way to reduce doubt on a massive scale and sometimes even stimulate societal progress. It is carried out by those who consider their beliefs to be good or effective, and the opinions of minority or deviant groups are sacrificed for the interest of the dominant group. However, not all views can be suppressed, since it requires an extreme amount of energy to externally force an individual to change internally. Thus, method of authority also has its limitations.

A Priori Method

Both methods of tenacity and authority aren't effective in the point of view of an individual's reason. A priori method, however, deductively develops beliefs from a set of foundational propositions. This method is much more comfortable to our intellect as it is rationally developed from a premise that the individual finds agreeable. However, these propositions are inherently subjective, which explains the extremely divergent views that exist in philosophy. This is most evident in metaphysics where subjective intuitions about our universe created various views even within a single era (e.g. Plato's idealism vs. Aristotle's realism).

Method of Science

The concept in contrast to a priori is a posteriori, which is the method of induction through empirical observations. According to Peirce, the method of scientific investigation can be used to establish an "external permanency" that is unaffected by humans but capable to influencing our thoughts at the same time. Although this external permanency won't be perceived in the same way, all individuals arrive at the same ultimate beliefs by taking into account the laws of perception. Therefore, the scientific method can be useful as an alternative to the method of authority in creating a collective state of belief without doubt, which Peirce thought would instigate societal and intellectual progress.

The method of science is also not without its flaws—it presupposes various conditions such as the existence of objective reality and truth. Peirce was well-aware of these arguments but argued to pay attention to the enormous progress that has been already made through science, technology, and medicine. Although he regarded all methods to be useful in different situations, the method of science was considered the prime method of intellectual investigation. This idea formed the basis for pragmatism, which is considered the first significant American contribution to philosophy.