Full Idea
A new opinion counts as 'true' just in proportion as it gratifies the individual's desire to assimilate the novel in his experience to his beliefs in stock.
Gist of Idea
New opinions count as 'true' if they are assimilated to an individual's current beliefs
Source
William James (Pragmatism - eight lectures [1907], Lec 2)
Book Reference
James,William: 'Pragmatism - eight lectures' [Dover 1995], p.25
A Reaction
Note the tell-tale locution 'counts as' true, rather than 'is' true. The obvious problem is that someone with a big stock of foolish beliefs will 'count as' true some bad interpretation which is gratifyingly assimilated to their current confusions.