Full Idea
I know the truth of the sentence 'I am here now' a priori, but I do not know a priori 'McGinn is in London on 15th Nov 1981'.
Gist of Idea
I can know indexical truths a priori, unlike their non-indexical paraphrases
Source
Colin McGinn (Subjective View: sec qualities and indexicals [1983], 3)
Book Reference
McGinn,Colin: 'The Subjective View' [OUP 1983], p.42
A Reaction
I'm not convinced that I can grasp the concepts of 'here' and 'now' (i.e. space and time) by purely a priori means. But he certainly shows that you can't glibly dismiss indexicals by paraphrasing them in that way.
Related Idea
Idea 18423 All indexicals can be expressed non-indexically [Cappelen/Dever]