Facets of Realism
It is usual to distinguish at least three types of realism: ontological, epistemological, and methodological realism. What do they say?
Ontological (or metaphysical) realism: There is a real world „outside".
It is there even if I don't look and even if nobody looks, and it was there before there were living or conscious beings. This world is the result of a long evolution. It is structured in time and space, by matter and energy. Its existence and structure does not depend on conscious or knowing systems, in particular not depend on human beings.An alternative position would be idealism: The world is (nothing but) a creation of my mind. My mind could exist even if there were no matter. Such positions were invented or even defended by philosophers like George Berkeley, Immanuel Kant, Friedrich Wilhelm Schelling, Georg Wilhelm Friedrich Hegel, Arthur Schopenhauer.
Epistemological realism: This world is knowable, at least in parts and approximately. It is reconstructible from its interactions with cognitive systems.
An alternative is positivism in its different forms as operationalism, logical empiricism, constructivism, especially radical constructivism, conventionalism. Positivists were Ernst Mach, Ludwig Wittgenstein in part, Percy Williams Bridgman and several members of the Vienna Circle; a conventionalist - at least with respect to the geometrical description of the world - was Henri Poincare.
Methodological realism: Scientific theories describe (i.e. reconstruct, predict, retrodict, explain) structures of the real world. The termini „true“ and „false“ are to be understood in the sense of correspondence theory: A statement is factually true if and only if the real world has indeed the properties ascribed to it by the statement. (In the long run we search not only for true, but for minimal descriptions of the world.)
An alternative is instrumentalism: Theories are (nothing but) economic condensations of past experiences and useful instruments for the prediction (or avoidance) of future events.
Instrumentalists, at least in some sense, were Andreas Osiander (1498-1552), in his strive to present Copernicus’ system as a useful model of the world without truth pretension), John Dewey (1859-1952), thinking and cognition being instruments for coping with and adapting to the world).These three kinds of realism—ontological, epistemological, methodological— depend on their respective predecessors: We cannot perceive or know something if it doesn’t exist, and we cannot recognize a factual statement as true if the objects talked about don’t exist. It is true: even the hardest realist cannot prove that the three principles presupposed by him are true. But that any of them is false cannot be proved either. Therefore the realist should present his principles not as certain, but as useful presuppositions of his worldview.
We might be tempted to compare the realist’s position with that of Gorgias of Leontinoi (ca. 480-380b.c.), a well-known sophist who declared: „There is nothing. If there were something, it could not be recognized. And if it could be recognized, it could not be communicated.“ With some tolerance we could relate the realist’s three principles to Gorgias’ three negations. (The third element does not correspond exactly.) We may conclude that the problems concerning realism and its critiques did engage philosophers since long. And we might wonder that the relevant problems are still not solved. Let’s try at least to collect some arguments in favour of realism.
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