Knowledge of the External World

What do we really know about the world in which we live? How do we arrive at our understanding of the world? Can we really trust our senses? Can we trust the information they provide us with? What does it mean if we cannot trust this data?


This unit explores in greater detail the epistemological account of knowledge that is empiricism! It raises both epistemological and metaphysical questions concerning the nature and extent of human experience.


In this module you will study the following the philosophical ideas of


Realism | Scepticism | Idealism


Click on the above links to be taken to these sections.


The department is aiming to update these topics so that you will be able to access information about your course from this website. If you cannot download something or are having problems using the site, please contact Mr. Winter.


  • What are the immediate objects of perception?
  • Do physical objects have the properties we perceive in them?
  • Is the common-sense view naïve?
  • Do sceptical arguments cast doubt on the common-sense view?
  • The secondary qualities thesis: does this establish that only the primary qualities of objects are objectively real?
  • What are the characteristics of primary and secondary qualities?

Sceptical Arguments

  • Do sceptical arguments establish the sense-data theory?
  • What are examples of sceptical arguments?
    • Illusion, perceptual variation, science inspired arguments, time lags.
    • How do these inform our understanding of the world?
  • What differences are there between sense-data and physical objects?
  • Could we know of a relation between sense-data and physical objects?
  • Could the existence of the external world be a hypothesis?


  • Should physical objects be regarded as collections of ideas/sense-data?
  • Are there good reasons for accepting idealism, eg solving the problem of material substance, consistency with empiricism, no linking problem?
  • What are the inherent difficulties with idealism?
  • Do these arguments cause us to disregard idealism? For example the problem of unperceived objects, availability of simpler, more systematic alternatives and confusion in the use of the term ‘idea’.