The work is divided in two parts. The first part is devoted to the exposition of what I call The Classical Concept of Substance. This Classical Concept of Substance is a generalized form of the concepts of substance entertained by Plato, Aristotle Descartes and the early Wittgenstein. By an examination of the notions of substance that these philosophers had -- how they conceived substances and why they postulated them -- I arrive at the general concept of classical substances common to all of them. This Classical Concept of Substance is the concept of an entity which is one, simple, existent, objective, and subsistent in an absolute manner. These substances were thought to be either themselves essentially intelligible or responsible for whatever intelligibility there is in the world, and their existence was thought to be a necessary condition for the possibility of knowledge and the necessary and sufficient condition of the intelligibility of the world. This is why any plausible account of human knowledge of the world appeared to require the postulation of these metaphysical entities. In the second part of this work I show that there is no need to advance the thesis which postulates the existence of classical substances. The reasons why the thesis was advanced that otherwise knowledge would be inconceivable -- can be met without having to postulate the existence of any metaphysical entities. Objects of reference suffice to perform the role that classical substances were supposed to perform. This is accomplished by proving two things: 1) that objects of reference are, strictly speaking, substances, for they have all the essential properties that belong to substances with the exception of one feature: while classical substances were supposed to be absolute entities, objects of reference have their substantial features in a relative manner, 2) that it is not a necessary condition for the being of knowledge that objects of reference should be absolutely substantial. The fact that they are only relatively substantial suffices to account for the intelligibility.of the world and the possibility of knowledge. The most important aspect of this thesis is the analysis of the substantial character of objects of reference as relative to the occasions on which the referring acts that mention them occur. This uncovering of the substantial quality of objects of reference, the rejection of the Classical Concept of Substance in favor of the concept of an object of reference is the main objective of this thesis.