It must be emphasized that there is no universally accepted and precise definition of ‘substance’. Depending on how one understood the word (or the concept) one might say either that Hume denied that there were any substances or that he held that the only substances (or the only substances of which we have any knowledge) were impressions and ideas. It would seem, however, that most philosophers who are willing to use the word ‘substance’ at all would deny that any of the following (if they exist) are substances: