Robert Paul wrote: "[Meter defined by light travelled over a period of time] may be what it is now, but as this is a contingent truth based on stipulation (is this what's meant by 'synthetic a priori'?), it could change next week." I agree and so my original comment is misleading. I should have said that the current common definition of the length of the meter refers to time. My point, however, stands: one cannot define the length of a meter except by ultimate reference to something that is not itself a length. Sincerely, Phil Enns Toronto, ON ------------------------------------------------------------------ To change your Lit-Ideas settings (subscribe/unsub, vacation on/off, digest on/off), visit www.andreas.com/faq-lit-ideas.html