The inference engine is a machine that accepts Assumptions, Queries, and Data, and produces Testable implications, Estimand, and Estimate. The implications and estimand do not necessarily need to be presented at the end, but they are both implicit within the model. The first of the outputs is a Y/N decision as to whether the given query could be answered under the existing causal model, assuming perfect data. If the answer is Yes, the inference engine next produces an Estimand, a mathematical formula that generates the answer from any hypothetical data. If the answer is No, then the engine returns to the assumptions stage to refine the model, through either simplifying assumptions or adding new scientific knowledge. Finally, after the inference engine has received the Data, it will use the Estimand to produce an actual Estimate for the answer, along with the amount of uncertainty in that estimate.