Full context:   Bertrand Russell wrote: Christians hold that their faith does good, but other faiths do harm. At any rate, they hold this about the communist faith. What I wish to maintain is that all faiths do harm. We may define "faith" as a firm belief in something for which there is no evidence. Where there is evidence, no one speaks of "faith". We do not speak of faith that two and two are four or that the earth is round. We only speak of faith when we wish to substitute emotion for evidence. The substitution of emotion for evidence is apt to lead to strife, since different groups substitute different emotions. Christians have faith in the Resurrection; communists have faith in Marx's Theory of Value. Neither faith can be defended rationally, and each therefore is defended by propaganda and, if necessary, by war.