The purpose of this book is to show thatmetaphysics plays an essential role in empirical inquiry and it is necessary to deal with the objection that, in the ordinary way, physics is sharply distinguished from metaphysics. Not only the 'plain man' but also many working scientists take physics to be a controlled discipline whereas they take metaphysics to be, at best a matter of speculation - the former concerned with facts, the latter with fancies. Today many would assert that metaphysical theorizing along with religous belief can only corrupt objective scientific thought and undermine scientific methodology. We have seen that though Renaissance and post-Renaissance philosophers (such as Copernicus and Descartes) undermined religious dogmas they did not dismiss religious faith; it gave essential support for their belief in Man's capacity to understand the world. The real separation of religion and metaphyhsics from science started with the Enlightenment and was made explicit by positivists. That positivist outlook is still influential today.