1. How Can We Know Anything about the World Around Us? Idealism: we can know about the world because it is comprised of our ideas Phenomenalism: physical objects are knowable, but only as bundles of sense data Naïve Realism: we do not perceive ideas or mental representations

2. Idealism: George Berkeley (1685-1753) What we perceive is the real world, but the only things we perceive are our ideas. So the world consists only of ideas and the minds that perceive them (including God). That is, the world’s existence consists in its being perceived (esse est percipi) –Objection: this seems to deny that physical bodies exist

3. Phenomenalism: John Stuart Mill (1806-73) Things are knowable because they are simply phenomena (things that appear to us under certain conditions) We know things in the world because they are “permanent possibilities of sensation” –Objection: things don’t exist because they are experienceable; they are experienceable because they exist

4. Transcendental Idealism: Immanuel Kant (1724-1804) We know about things not as they are in themselves but only as they appear to us (as phenomena), structured by the mind’s categories (e.g., space, time, cause) –Objections: (1) If we are limited to phenomena, we can’t know what the world is really like; (2) categories differ culturally; (3) this does not explain why we have only these categories

5. Naïve Realism: We Do Not Perceive Ideas; We Perceive Their Objects Perceptions are always “intentional,” that is, about something; and when our perceptions are caused by the things they are about, we can be said to know those things Perceptions are not purely passive; they are affected by one’s background knowledge and beliefs John Searle