Foundationlism refers that which can be perceived to be self evident principle. Any argument or item require strong holding. Descartes use the method of doubt to make this argument. He doubts beliefs, his senses such as taste, smell, touch, sight and hearing. The only thing that he holds without doubt is that he exists as a being that thinks. He describes the causal non inferiority principle by saying that effect cannot have more reality or perfection than the cause. He uses this as a premise for the concept of perfect being. He perceives the world and himself as imperfect and therefore there must be an existence of perfect being that caused the perfect concept. This makes him not doubt the existence of God and also that He is not a deceiver as this would make Him imperfect. It is therefore very hard to doubt existence of God because of the many effects that are self evident. He therefore says that all mistakes made in science is simply because at the beginning conclusions about something were made too fast without clear and distinct information.
David Hume was one of the philosophers who wrote on metaphysics, he made it clear that unless we understand the causal connections of event of things all knowledge is empirical and deductive and thus uncertain. He bases his argument on the sense of experience. He argues that to show the relation between the ideas expressed by analytic sentences and matter of fact expressed by synthetic sentences requires sense of experience. The knowledge acquired through experience and our judgment about cause and effects can then be said to be s viable. The critique of knowledge being based on the experience was that, the future resembles the past. It is therefore not conclusive to base our argument on the past trying to justify the future or present. However, this argument is very important if we have to consider the ideas that people ever come up with, leading people to want to know the truth about something and hence advancement of the knowledge. The lack of surety of the scientific knowledge has great impact on our belief in the possibility of metaphysics and truth of science leading to great skepticism.