whether they are actually to be found in the nature of the things outside of us." Berkeley George Berkeley wrote his famous critique of this distinction in his book Three Dialogues between Hylas and Philonous. Berkeley maintained that the ideas created by sensations are all that people can know for sure. As a result, what is perceived as real consists only of ideas in the mind. The crux of Berkeley's argument is that once an object is stripped of all its secondary qualities, it becomes very problematic to assign any acceptable meaning to the idea that there is some object. Not that one cannot picture to oneself (in one's mind) that some object could exist apart from any perceiver — one clearly can do this — but rather, that one cannot give any content to this idea. Suppose that someone says that a particular mind-independent object (meaning, an object free of all secondary qualities) exists at some time and some place. Now, none of this particularly means anything if one cannot specify a place and time. In that case it's still a purely imaginary, empty idea. This is not generally thought to be a problem because realists imagine that they can, in fact, specify a place and time for a 'mind-independent' object. What is overlooked is that they can only specify a place and time in place and time as we experience them. Berkeley did not doubt that one can do this, but that it is objective. One has simply related ideas to experiences (the idea of an object to our experiences of space and time). In this case there is no space and time, and therefore no objectivity. Space and time as we experience them are always piecemeal (even when the piece of space is big, as in some astronomical photos), it is only in imagination that they are total and all-encompassing, which is how we definitely imagine (!) 'real' space and time as being. This is why Berkeley argued that the materialist has merely an idea of an unperceived object: because people typically do take our imagining or picturing, as guaranteeing an objective reality to the 'existence' of 'something'. In no adequate way has it been specified nor given any acceptable meaning. As such Berkeley comes to his conclusion that having a compelling image in the mind, one which connects to no specifiable thing external to us, does