In his seminal essay "Religion and Respect" Cambridge Professor of Philosophy Simon Blackburn ventures a secular definition of the sacred: "To regard something as sacred is to see it as marking a boundary to what may be done. Something is regarded as sacred when it is not to be sacrificed to other things, not to be weighed in a cost-benefit analysis, not to be touched". In a free civilised society, freedom of speech is sacred in this sense. The Paris assassins have crossed the boundary and attacked one of our sacred values and this is not to be tolerated. Many of our forebears died to establish freedom of expression as a sacred value and we must honour their sacrifice by defending it with all the strength we can muster.