Philosophical vocabulary

In the later part of section 2 Hume talks about the philosophical vocabulary between the term impression and the term idea. As he states earlier in the section for the use of the words an impression is are clear and exact, things that we percieve with our senses, taste, touch, and so on. Ideas are less vivid, faint and some times obscure and unlike impressions we are likely to suffer error in remembering them. So when talking about an idea in philosophical terms we may ask by what impression did this idea come from. If it were to not come from an impression it would then be useless and meaningless.