Russell's Construction of the "external World"

2) Explain Russell’s construction of the “external world”, i.e., the things we see and touch.

In Our Knowledge of the External World Russell aims to show that physical objects are logical constructions out of actual and possible sense data, where each man's sense data form an extended world. Russell says that there are no sense data that are common to two private worlds, but there are correlations between similar sense data in the various private worlds. These correlations are things, being that a thing is the class of all the similar sense data in the entire private world. Russell asks, how can we come to know things about the physical world through the actions of our senses? And if so, how do we know these things? Russell uses the concept of sense data to explain this and assumes that all human knowledge must begin with sensory data experience. Sense data are the subjective, mind dependent occurrences of perception that supposedly provide us with knowledge of a mind independent physical world. They are the characteristics and qualities we primitively and immediately sense about physical objects: color, shape, texture, temperature, and so forth. This sense data provide the primitive content of our experience, and for Russell these sense data are not merely mental events, but rather the physical effects caused in us by external objects. Take matter for example. Matter is to be understood as that which physics is about. So, matter must be such that the physicist can know its existence. In other words, what physical science is concerned with and makes discoveries about must be a function of the physicist’s sense data. What could that function be? There are only two ways in which we can know the existence of something. They are either immediate acquaintance, which assures us of the existence of our thoughts, feelings, and sense-data, or they are general principles according to which the existence of one thing can be inferred from that of another. The bridge which relates the one’s sense-data to the external world must correspond to one of these ways of knowing that something exists. If our knowledge of the external world can be reduced to what we know by acquaintance, then things like matter should be understood as a logical construction out of sense data. Otherwise, it must be by inference that we know the existence of something. So according to Russell the construction of a thing must be found through either logical construction or inference.

Moving on from sense data, Russell outlines a way of constructing a common physical and geometrical world out of the private experiences of different perceivers, where each perceiver looks at the world from one particular perspective. Russell compares these perspectives to Leibniz' monads, where the external world is constructed out of the different monadic perspectives and each perspective is determined thereby. Hence a sufficient partial