• Our conception of an item is an idea pertaining to it from sense-data
  • Is matter real? What is its nature?
  • Bishop Berkeley, Leibniz and other Idealists believe there is ‘matter’ or ‘the real object’ but believe that our sense-data does not reveal its true nature; what appears as matter is mental. deny existence of matter as something different from mind

    • Matter could be ideas in the mind of god, or the collective mind of the universe
  • Descartes - “cogito, ergo sum” - “I think, therefore I am.” - systematic doubt
    • he used a system of doubt, believing in only what was clear to him to be true. this led him to doubt the existence of everything but his own self, clearly true because he is experiencing things
    • If something can be doubted, it should be doubted, until there is a reason not to doubt it.
  • Public neutral objects must exist over and above the sense-data, since there is a shared conception of the physical object between minds who are all seeing the object slightly differently (private sense-data) from a different visual perspective etc etc
    • While people see slightly different things it is easy to arrive at a proper object because the perspectives fallow the law of perspectives, refraction of light etc
    • When buying a table from a friend, you purchase the table, not your friend’s sense-data of the table. Though he did by the confident expectation of relatively similar sense-data
    • In trying to prove the existence of public permanent objects, you cannot appeal to the testimony of other people, as this testimony itself consists of sense-data (we have no reason to believe the people exist!)
    • Supposing there are physical objects rather than everything being a conception of our own mind is more simple
      • If you look a cat moves from one part of a room to the other, it is simpler to assume that it moved to a set of intermediate positions, but if it is just sense data that teleported then popped out of existence when you stopped looking this is complicated.
      • We also intuitively understand how a cat gets hungry between meals, this is ridiculous if the cat doesn’t really exist since no hunger but your own can be sense-datum to you. How would its hunger grow when you are not seeing it, if it is not in existence?
  • Objects are not the same as sense-data but they are coressponding
  • Dreams give us slight doubt of this, but generally we can believe there is a real world existing outside our perception
  • When sense-data stops existing we believe thta probably the thing does not stop existing.

Philosophy can organise instinctive beliefs, ideally into a harmonious system

  • there can never be a reason for rejecting an instinctive belief unless it clashes with others; we cannot have reason to reject a belieef except on grounds of some other belief

light as a wave means that waves are the cause of our physical sensation of light (a blind man could understand a wave, but not the sensation of light a seeing man receives as sense-data) our experience of light is not supposed by science to form any part of the world which is independent of us and our senses;not only sites and sound but also our sense of space as we get it from sense data. space of touch and sight are different, but in actuality neutral between them.

  • time and space remain in order between public and private

  • Whatever exists must be in some sense mental
  • bishop berkely thinks anything conceivable must be in yours or another mind
  • ‘idea,’ what is immediately known e.g. sense data memory imagination
  • we only know of the tree what our sense data sees; whatever is known is ideas
  • it only continues to exist because it is perceived in the mind of god


  • a tree is not in the mind; the thought of a tree is in your mind

knowledge of truth (!error) & knowledge of sense-data knowledge of things and of truth table physical object is knowledge by description described by acquaintance sense data direct knowledge the true object is only known by description (truths)

knowledge of truth and of things lies on acquaintane

acquaintance by memory, introspection (me desiring food as object) acquaintrance of universals (whiteness, diversity); if we are aware of it it is a concept when we look into ourselves we see a particular thought or feeling - not the true ‘I’

a man (ambiguous) the man (definite)

“Every proposition which we can understand must be composed wholly of constituents with which we are acquainted” we can have knowledge by description of things we have not experienced