  We present a non-naive version of the Precautionary (PP) that allows us to
avoid paranoia and paralysis by confining precaution to specific domains and
problems. PP is intended to deal with uncertainty and risk in cases where the
absence of evidence and the incompleteness of scientific knowledge carries
profound implications and in the presence of risks of "black swans", unforeseen
and unforeseable events of extreme consequence. We formalize PP, placing it
within the statistical and probabilistic structure of ruin problems, in which a
system is at risk of total failure, and in place of risk we use a formal
fragility based approach. We make a central distinction between 1) thin and fat
tails, 2) Local and systemic risks and place PP in the joint Fat Tails and
systemic cases. We discuss the implications for GMOs (compared to Nuclear
energy) and show that GMOs represent a public risk of global harm (while harm
from nuclear energy is comparatively limited and better characterized). PP
should be used to prescribe severe limits on GMOs.
