Why do some individuals cooperate with their fellow human beings while others take advantage of them? The human drive for cooperation and altruism is one of the most powerful forces shaping our society, but there is an enormous behavioral variance in individual behavior. At the same time, whether it is intuitive to behave in a cooperative manner or whether such behaviors are calculated deeds remains an unanswered question. Indeed, recent empirical investigations regarding the spontaneity of human cooperation have found mixed evidence, possibly due to a failure to induce compliance in the behavioral manipulations employed. We conducted a laboratory experiment inducing intuitive and deliberative behavior through gradual economic incentives that ensure compliance. To account for individual heterogeneity, we independently measured social value orientation and aversion to interpersonal (strategic) uncertainty. We find that these measures determine the intrinsic predisposition towards cooperation. Subjects with more altruistic social values or a higher tolerance towards interpersonal uncertainty are more cooperative. Crucially, we find causal evidence that there is no universal default mode of behavior. Rather, intuition enhances intrinsic predispositions, while deliberation moderates them towards socially acceptable behavior. That is, subjects with a higher (resp. lower) predisposition towards cooperation became more (resp. less) cooperative under time pressure compared with time delay.