While the minimum number of bikes one should own is three, the correct number is n+1, where n is the number of bikes currently owned. This equation may also be re-written as s-1, where s is the number of bikes owned that would result in separation from your partner.
Velominati - Rule #12
Volume 15, #11 - Making NS a Bicycling Destination
IN THIS EDITION:
Making Nova Scotia a Bicycling Destination