Mental model (Johnson-Laird, 2001) and probabilistic theories (Oaksford & Chater, 2009) claim to provide distinct explanations of human reasoning. However, the dual strategy model of reasoning suggests that this distinction corresponds to different reasoning strategies, termed "counterexample" and "statistical," respectively. There is clear evidence that most people have a preference for a given strategy, and that this predicts performance on a variety of forms of reasoning and judgment (Thompson & Markovits, 2021). To date, however, the evidence for this conclusion has been correlational in nature; in the current studies, we manipulated strategy use. To this end, we gave people (N = 885) explicit instructions to reason either using a counterexample strategy or a probabilistic strategy. In two studies, we observed that the ability to follow these instructions was constrained by people's spontaneous strategy use, and that the effect of instructions carried over to two subsequent forms of reasoning (a) belief-biased inferences and (b) base-rate judgments. Finally, the ability to follow instructions was correlated with reasoning accuracy on both tasks. These results provide strong evidence for the underlying reality of the dual strategy model and show that explicit instructions to reason differently can modify performance on different forms of reasoning.