<标题> People created proverbs and used to apply them when experiences similar to the one which resulted in the construction of the proverb reoccurred. The Persians had one of the most famous proverbs that are still used in our time; they used to say “doubt is the key to knowledge”, but to what extent is this phrase true? Through the areas and ways of knowledge, this proverb will be further studied to determine to which extent it is true. In this essay, I will be using the natural sciences and religion as areas of knowledge and linking them to the ways of knowledge; perception and reason or logic.Doubt is one of the earliest ways the human beings started gaining knowledge from the world around them. It is known that doubt is when a person starts questioning a subject that confused him or has been on his mind for a time. It is then that this person starts asking questions in order to gain further knowledge about the subject he wishes to acquire. We can generally say that doubt is the origin of obtaining knowledge as human beings started questioning the world and everything in it; they were able to get the answers they wanted and increased their knowledge. The world famous French philosopher, writer, physicist and mathematician René Descartes believed that doubt could never be the key to knowledge and information from the world. He was considered one of the first thinkers ever to introduce philosophy to natural sciences. Descartes believed that one can gain truth without doubt; he introduced his method called “methodological skepticism” in which he rejects any ideas that can be doubted, then reestablishes them so that he can get genuine knowledge from these ideas. One of Descartes’ books is one called “Meditations on First Philosophy”. The book has six meditations in it in which Descartes banishes any belief that contains, even if in small quantities, any kind of uncertainty, but then reestablishes the things that are known for sure. Each one of the six meditations were written as if in one day Descartes speculated and came up with the meditation; so the book was authored as if he meditated for six days and developed his meditations.