  Once the concept of a sense-datum has been introduced in this way, it is easy to see that false appearances can be handled by distinguishing between the properties of sense-data we apprehend and the properties of the physical objects which give rise to these sense-data. But what is the relationship between sense-data and physical objects? Moore took it that there are three serious candidates to be considered: (i) an indirect realist position, according to which sense-data are non-physical but somehow produced by interactions between physical objects and our senses; (ii) the phenomenalist position, according to which our conception of physical objects is merely one which expresses observed and anticipated uniformities among the sense-data we apprehend; (iii) a direct realist position, according to which sense-data are parts of physical objects — so that, for example, visual sense-data are visible parts of the surfaces of physical objects. The indirect realist position is that to which he was initially drawn; but he could see that it leaves our beliefs about the physical world exposed to skeptical doubt, since it implies that the observations which constitute evidence for these beliefs concern only the properties of non-physical sense-data, and there is no obvious way for us to obtain further evidence to support a hypothesis about the properties of the physical world and its relationship to our sense-data. This argument is reminiscent of Berkeley's critique of Locke, and Moore therefore considered carefully Berkeley's phenomenalist alternative. Moore's initial response to this position was that the implied conception of the physical world was just too ‘pickwickian’ to be believable. This may be felt to be too intuitive, like Dr. Johnson's famous objection to Berkeley; but Moore could also see that there were substantive objections to the phenomenalist position, such as the fact that our normal ways of identifying and anticipating significant uniformities among our sense-data draw on our beliefs about our location in physical space and the state of our physical sense-organs, neither of which are available to the consistent phenomenalist.