Hence my argument is not some simple deduction: minds are brains, so constructive realism is true.
Rather, like all inferences, my conclusions are justified by overall coherence: given that minds are brains, and given everything else we know, the most coherent conclusion is that people use perception and inference to the best explanation to construct knowledge about reality.
This process of justification will seem circular if you think that knowledge should have a foundation of indubitable truths from which other truths are derived.
But no one has ever succeeded in identifying such a foundation in either sense experience or a priori reasoning, so we have to strive instead to construct the most coherent systems of representations that we can.