'Tabula rasa' theory.
Tabula rasa means 'blank slate', which stand for an idea that every idea of an object or even that we have is built up on experience that we had with that object or event. This idea is supported by philosophers John Locke (1632-1704) and David Hume (1711-76).
Hume's reasons for saying 'every idea ... is copied from a similar impression'.
Hume was developing Locke's idea that everything that we have on our mind is based on our expirience. Without an experience we are unable to correspond to an idea. The following extract proves this Hume's view:
'If it happen, from a detect of the organ, that a man is not suspectible of any species of sensation, we always find that he is as little suspectible of the correspondent ideas. A blind man can form no notion of colours; a deaf man of sounds.'
In this extract it is proved that without a sence of sight or sound you are not able to have an idea of colours or sounds.
How Hume tells difference between 'impressions' and 'ideas'.
An impression is a far more strong feeling than an idea, as it is 'all strong and sensible' and 'admits not of ambiguity', also they may 'throw light on their correspondent ideas'. An idea is a 'lighter' version of what a person felt when having an experience, ideas are 'naturally faint and obscure'. Actually, an idea is based on an impression and to Hume's view it isn't 'easy to fall into any error or mistake with regard to them' (impressions). In other words, it is difficult not to see any difference between an impression and an idea, as only 'disordered by disease or madness' will not be able to do that.
Hume's account on how imagination works and why does Hume need to give an account of the imagination.
Sometimes an idea can appear without having an experience that it was based on. There was an example of 'a golden mountain' - everyone can surely imagine it at some point even though nobody have actually experienced it, simply because such thing does not exist. Yes, we could interpret this as a combination of two ideas of a mountain and a gold, though the idea of a golden mountain would be stringer if we had experienced it. However, we still may have an idea of a golden mountain through an experience happening in our minds and imagination is the key. Imagination 'escapes all human power and authority' and also 'is not restrained within the limits of nature and reality'. But still, if we look at the imagination process in depth, we would see that it's 'confined within narrow limits', because our imagination is still based on what we experienced and sensed.
The philosophical significance Hume draws from his analysis of the origin of ideas.
The perception of the world around us comes from our ideas and experiences. Our mind is a blank page, we fill it with ideas, which we get from our experiences. Experiences provide 'strong and vivid' impressions which clarify an idea, which itself is 'naturally faint and obscure ... apt to be confounded with other resembling ideas; and when we have often employed any term, though without any distinct meaning, we are apt to imagine it has a determined idea annexed to it'. 'Words in their primary or immediate signification, stand for nothing but the ideas in the mind of him that uses them', which simply means that words are created just to indicate an idea. However, the perception is also based on our imagination, which helps us to have an idea of some things that we have not experienced. Though Hume argues that imagination itself is 'no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience'.