Wikipedia
"Dispositionist" is a term in Social psychology used to describe those that believe people's actions are conditioned by some internal factor, such as beliefs, values, personality traits, or abilities, rather than the situation they find themselves in.
A Disposionist is a person who believes in Lay Dispositionism, the tendency to use personality traits or other dispositions (e.g., intelligence) to explain and predict social actions or outcomes (Ross & Nisbett,1991).
For example, a dispositionist might explain bankruptcy as the largely self-inflicted result of personal laziness and/or imprudence. Situationists, in contrast, view bankruptcy as frequently caused by more complicated external forces, such as divorce or the medical and other costs of unanticipated illness.
Another example of this concept is when a person doesn't eat pork. When they order a sandwich at a restaurant and it comes with bacon on it, they order the sandwich without bacon. When they receive the sandwich and it has bacon on it anyway, they ask for a new one instead of picking the bacon off.
Lay dispositionism has been evaluated in relationship to implicit theories of personality.
(See also: fundamental attribution error).
The opposite of dispositionism is " situationism".