Epistemology is the philosophical investigation into the nature of knowledge and justified belief produced by means which are reliable in the circumstances. Epistemology primarily addresses the following questions: “What is knowledge?”, “How can we justify our claims to knowledge?”, and “What can we know?” Philosophers have argued different positions that are canvassed in the Philosophical Investigations. Typically, philosophers have first argued for the view that knowledge is justified true belief and then gone on to ask the question “What kind of justification do we need in order to have knowledge?” Skeptics are convinced that it is impossible to know anything. Some philosophers try to demonstrate that we can be sure about some things. Arguments used against rivals may result in a change of position on philosophical views about justification (Appiah 39).
Typically, epistemologists do not concentrate on acquaintance or procedural knowledge but stress upon propositional knowledge. A proposition is a declarative sentence expressing natural state of things/some generally accepted facts, or somebody’s opinion (that may be wrong as well), e.g. “Dolphins are mammals,” “It is wrong to insult the weaker.” Presumably, propositional knowledge embraces knowledge from different fields of human activity; it may be of different types: geographical, scientific, mathematical, self-knowledge. Generally speaking, man can learn any truth; nonetheless, some truths may be inconceivable. One of the most acute epistemological concerns is to define the peculiar features of knowledge, so that one may know what he/she can or cannot cognize. To put it another way, epistemological studies, in primary respects, presuppose meta-epistemological studies – what a human can know about the essence of knowledge (plato.stanford.edu.).
Depending on the source of the knowledge, propositional knowledge may be of two types: a priori or non-empirical knowledge and a posteriori or empirical knowledge. The first type exists regardless of any experience, and reasoning serves as a prerequisite for it. To exemplify non-empirical knowledge, let us refer to logical truths (e.g., the non-contradiction law) or knowledge of abstract pretensions (ethical pretensions or claims about varied conceptual issues). Empirical knowledge results from an immediate sense experience (although reason is also present in this case). For instance, having seen an object, one knows its shape, color, size, etc.; having visited some country, a person already knows something about its geographical location. Rationalists are convinced that all types of knowledge are possible only due to reasoning, whereas empiricists claim that only experience predetermines the possibility of knowledge (iep.utm.edu.).
Rene Descartes and David Hume have compared views on the origin and the essence of ideas and the ability of the human mind to understand new concepts. This ability seems to be rather specific since the human mind cannot apprehend itself. The truth, as fetched out by the two philosophers, is impossible without the senses. Following Appiah, let us quote Descartes’ thoughts:
According to Descartes the evil demon is powerful, clever and deceitful. It has devoted itself to deceit that there is an external world with people which is nonexistent. The demon may change the world at any moment so as to render a belief false. Further, the existence of a benevolent God, attempting to do the opposite of the demon, would not allow us knowledge of the world (Appiah 45, 51).
David Hume argues that knowledge cannot exist only on the ground of the senses since the latter give us only a partial picture of what really exists. Observing something, one may trust his/her senses and think that he/she already has knowledge of the world outside the piece which he/she is perceiving at the moment. Thus, Hume stresses that the senses should be supplemented with reason, which, in turn, cannot justify any belief about the outer world that stretches beyond the horizon of the immediate sense experiences. As Appiah mentions, “On the other hand, Hume states that to form inappropriate shapes and appearances, imagination is restrained within the limits of reality and nature (Appiah 51). Consequently, it can be reasonably said that the given piece of reality, which we perceive separately, cannot provide us with a clear overall picture.
Metaphysics is an area of philosophy that studies existence. The word “metaphysics” firstly appeared as the name of Aristotle’s book. It is concerned with the following questions: “What is existence?”, “Do numbers exist?”, “Does God exist?”, “Is God’s existence a necessary truth?” (Appiah 299). According to Appiah,
It [metaphysics] encompasses everything that exists, as well as the nature of existence itself. It says whether the world is real, or merely an illusion. It is a fundamental view of the world around us. Metaphysics has become the label for the study of things which transcend the natural world. (Appiah 300)
The question about God’s existence can be answered positively with the help of ontological arguments. As far as Appiah’s ideas are concerned, the ontological arguments proving God’s existence by reason are not dependent on any definite fact of the actual reality, but are to be applied in any probable world. Ontological arguments imply that man knows that God exists in the same way that he knows that 2 + 2 = 4: through mere reason. In other words, they lack any background (observation or experience); yet these arguments tend to demonstrate God’s existence (Appiah 311).
Practically, these arguments are based on reason alone, thus, they arise from nothing but are a priori and analytic in their essence. The primary and most famous ontological argument was offered in the 11th century A. D. by St. Anselm of Canterbury. He claimed that God’s existence may be derived from the notion of a “being than which no greater can be conceived” (stanford.edu.). St. Anselm argued that, suppose such a being does not exist, then a greater one – a being than which no greater can be conceived, and which really exists – can be cognized. However, such state of things is absurd: there does not exist anything more magnificent than a being than which no greater can be conceived. Consequently, a being than which no greater can be conceived – God – really does exist (plato.stanford.edu.).
Rene Descartes makes use of the idea of a greatly perfect being. He mentions that one may cognize a greatly perfect being who does not exist in the same way as he/she conceives a triangle whose sum of interior angles does not make 180 degrees. Therefore, he suggests, for we cognize a greatly perfect being – we do have the idea of it – we are to come up with the conclusion that a greatly perfect being does exist. In his book, Appiah presents these Descartes’ thoughts in detail:
Descartes points out that if you imagine a triangle, one of its main properties is that it has three sides and three corners. These are the predicates of a triangle. Descartes expands his point, by referring to the properties of God. If something perfect is imagined, it must be even more perfect if it was in existence. Furthermore, the most perfect thing has all properties including existence. Descartes, therefore, believes that a perfect being has all predicates. For instance, if a perfect being has all predicates, one of the properties must surely be existence. If God is the greatest conceivable being and has all qualities, he must have all predicates, one of them being existence. Therefore God must surely exist. Descartes says, “nothing is greater or more perfect than it is, and there is nothing else that is great or perfect as it is.” (Appiah 312-313)
On balance, epistemology and metaphysics deal with the two different issues: cognition and existence respectively. Epistemology stresses upon the necessity to combine reason with the senses (thus, emphasizing both a priori and posteriori knowledge), which together can help to create the whole trustworthy picture of reality. Metaphysics, on the contrary, argues that things are unchangeable and must be conceived on the ground of reason only since empirical experience is unable to cognize the principles and origins of existence.