Full Idea
The cause of obscurity in simple ideas seems to be either dull organs, or very slight and transient impressions made by the objects, or else a weakness in memory, not able to retain them as received.
Gist of Idea
Obscure simple ideas result from poor senses, brief impressions, or poor memory
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 2.29.03)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.363
A Reaction
This seems to give some support to the epistemological view of vagueness, with the implication that if our senses and memory were perfect, then our ideas would have perfect clarity.