In many aspects of our lives, the use of faith as a basis of knowledge can be found. Whether it is faith in your teacher's advice, faith in a God, or faith in a scientific theory, it is there. But what is faith? A definition of faith in a theory of knowledge context is the confident belief or reliance in a claim of knowledge by a knower, without the knower having conclusive evidence. Indeed, if a knowledge claim is supported by evidence, then we would use reason rather than faith as our basis for knowledge. If we define knowledge as "true and justified belief", we can see that faith, being without justification, can never meet this definition and therefore cannot be used as a reliable basis for knowledge. However, the question arises: what happens if a certain claim to knowledge lies outside the realm of reason? What if a knowledge claim cannot be substantiated by empirical evidence and reasoning alone, like a religious knowledge claim? This is where faith allows the knower to decide what is knowledge and what is not, when something cannot be definitively proven through the use of evidence. When we evaluate faith as the basis of knowledge in the natural sciences, it appears that without faith in the research done before us, it is impossible to develop further knowledge from it. Yet at the same time, if we had unshakable confidence in existing theories, they would never be called into question, and thus our progress in knowledge in the natural sciences would come to a halt. Although I intend to approach this essay in a balanced manner, this essay may be subject to a slight degree of bias, due to my own non-religious viewpoint. Today, faith is the cornerstone of all major claims of religious knowledge, because there is no definitive certainty. way of...... middle of article ...... th in theory, it was replaced by cell theory and germ theory, allowing natural science knowledge to advance in these areas, ultimately leading to vaccine development and stem cell research. Although faith alone cannot be said to require truth, it is by no means useless as a basis of knowledge in the fields of knowledge of religion and the natural sciences. Faith allows the knower to make the decision of what is knowledge and what is not, even when the claim to knowledge cannot be justified by evidence or empirical reasoning. But simultaneously, this quality of faith makes it useless for finding absolute truth. In the natural sciences, faith can be considered both a necessity, because it is essential to the construction of knowledge, and yet it must also be questioned, because the progress of science requires the refutation of current theories..