Classical Rationalism The fundamental source of knowledge is reason. Knowledge should be of the essential properties of things. Such knowledge is knowledge of necessary truths. Sensory experience informs us of the world as it now and, via memory, it informs us of how the world has been. It cannot tell us how things must be or of the essential properties of things. Our senses are fallible, limited and subjective. Only reason can give us complete knowledge of the objective world. Necessary truths are knowable a priori. We have innate ideas (innate knowledge). Coming to know is either discovering what we already know or the result of reason using those materials t make new discoveries (as in maths).

RATIONALISM – PLATONIC MOTIVATIONS The senses inform us of a changing world. Reason grasps the underlying structure of the world. The senses are fallible. The senses can’t help us gain certain types of knowledge: e.g. mathematical. The analogy of the cave: ordinary mortals see only the shadows of reality.

Plato and the Forms Reason gives us knowledge of the forms – the essences of things. The Imperfection Argument: we know the geometric properties of circles even though we cannot experience them. The Epistemological Argument: if you know something, it must be true. So it must be necessarily true. But the senses can’t discover necessary truths. The Context Argument: whether a painting is beautiful or not cannot be discovered with the senses as people with the same experiences disagree. Before we were born, our souls lived in the world of forms. In this embodied life, our knowledge of the forms is buried and must be unearthed by exercising reason – doing philosophy. The One Over Many Argument: what makes two apples both apples is something they have in common. This thing cannot be discovered by the senses.

RATIONALISM – CARTESIAN MOTIVATIONS The senses are fallible and could be deceived. Science is not concerned with the sensible properties of things. It is concerned with quantifiable properties. Reason is required to work out the mathematical structure of the universe: e.g. the laws of physics. The senses inform us of a changing world. Reason grasps the underlying structure of the world. (Think of the wax example.) It is only through reason that I can be certain of anything: 1st: My own existence. 2nd: God’s existence. 3rd: God’s benevolence. 4th: My capacity for clear and distinct ideas.

Rationalism – Fundamental Motivations There’s an intuitive difference between the essential/necessary and accidental/contingent properties of things. People differ in all sorts of uninteresting ways. They are the same because they are all people. What makes someone a person? What is the essence of a person? This is a philosophical question. The essential properties of something make it what it is. Philosophers and scientists are interested in them. So how do we find out these philosophical facts about the essential natures of things? Rationalists say: through reason, not experience. Why? The senses are… 1. Fallible: We can make mistakes. We can be deluded (e.g. dreams, hallucination) They only work in certain conditions (e.g. when it is light) 3. Subjective: How can we tell that we experience the world the same way? 2. Limited: We can’t see atoms or the edge of the universe. The senses cannot tell us about the essences of things. Experience can tell me how things are now: e.g. this piece of metal conducts electricity. Many experiences can tell us how things are on many occasions: e.g. piece of metal 1 conducted electricity on 1/2/07 piece of metal 2 conducted electricity on 2/2/07 piece of metal 3 conducted electricity on 3/2/07 … and so on But only on finitely many occasions. But we want to know general or universal necessary truths: do all bits of metals conduct electricity? We can never verify by experience whether it is part of the essence of being a metal that it conduct electricity because we cannot check every bit of metal. So we can only discover general, necessary truths through reason. Problem 1 Problem 2

Descartes and our perception of the world Our innate ideas of colours are triggered by the information in the brain sent from the eyes The cube is red in the sense that it has a chemical structure that our brains react to with a sensation of red. It is not red in the way we experience it as red. Colourless matter:

Descartes and the wax Sight: bright yellow Smell: flowers Taste: pollen Sound: dull thud Feel: solid Sight: dull yellow Smell: none Taste: none Sound: none Feel: soft, malleable All that remains constant is occupancy of space by matter: extension

Chomsky and Rationalism How do children learn language so quickly? They can’t be blank slates. Children are rarely corrected. In some societies, children aren’t spoken to until they can speak back. We are born “knowing” the common grammatical structure to all human languages: UG (universal grammar) As we are exposed to a language, we can work out what particular type of grammar it has. Is he a rationalist? Do we have innate knowledge? Not really. We do not have this information as knowledge we can articulate. It is like hard- wired information. The Poverty of Stimulus argument: children manage to learn bewilderingly complex things with the minimum of input. So they must have some kind of innate knowledge of language that helps make the task easier. It is rare to hear the same sentence twice. So, children are producing sentences they have never heard before. They are not simply “copying”.