In its most radical version, the doctrine according to which all of our knowledge is confined to what we have contact with through sense experience (sense knowledge arising from the perceptions of the external and internal senses). Empiricism denies that such things as essences or natures can be known since they are not perceptible by the senses. Empiricists such as David Hume, however, hold that we can also know the relationships that the perceptions of the internal senses (what he calls “ideas”) have with each other.