A tendency to believe something.

Noun

bias (countable and uncountable, plural biases or biasses)

1. (countable, uncountable) inclination towards something; predisposition, partiality, prejudice, preference,predilection
   
   • 1748. David Hume. Enquiries concerning the human understanding and concerning the principles of moral. London: Oxford University Press, 1973. § 4.

     nature has pointed out a mixed kind of life as most suitable to the human race, and secretly admonished them to allow none of these biasses to draw too much

   • John Locke

     Morality influences men's lives, and gives a bias to all their actions.