Economics "speaks a narrow truth, and thinks it a broad truth." But Economics is not the only science to make that mistake, and that is precisely Newman's point. In the fourth discourse, Newman uses Nassau Senior's first lecture as an Oxford professor as an example of what might happen to all of us. Old Testament studies yield much truth: its very correctness convinces the scripture scholar that he can speak on economics. The anatomist discounts the soul, the historian discounts Revelation; both think that theology and economics surely exaggerate their claims. Political philosophy gives much wisdom, but not all wisdom. But the judgment of the relative value of a discipline does not belong to the discipline itself, but to a higher discipline, i.e., the Architectonic Science or Philosophy (cf. Idea, p. 68). According to Newman, political economy is

a science simply lawful and useful … at the same time dangerous and leading to occasions of sin … and in consequence, if studied by itself, and apart from the control of Revealed Truth, sure to conduct a speculator to unchristian conclusions. [The political economist, if he is to be at all at the service of truth] must of course direct his inquiries towards his end; but then at the same time it must be recollected, that so far he is not practical, but only pursues an abstract study. (Newman, Idea, p. 64, 66, emphasis added)

If I may be permitted a paradox, one "practical" goal of pursuing knowledge for its own sake is that of knowing the truth. We study economics for itself because we want to know the whole truth, not just a little part. The devoted study of philosophy, history, mathematics, or politics is just a "means" to knowing the whole truth—necessary means for us of limited minds, but not the end. The "practical" end of knowing a particular discipline is that it gets us a little closer to truth. So the study of economics "as an abstract study," is both a requirement and an obstacle to the practical end of all study: knowing the whole truth.

Even more, "practical" ends in the sense of the Useful—virtue, health, prosperity, roads and buildings—also require integration. As Marshall says, focus on the practical may force us to integrate too soon. They distract us from the pursuit of knowledge and so we talk to other disciplines before we have anything to say; the conversation ends up shallow and self-aggrandizing. On the other hand, applied research can be done after much basic research: integration need not be shallow. If basic research is done for its own sake, all the while hoping for eventual application (ten months, ten years, ten decades later), it will have to remain humble. Each researcher knows she is one part of a team of researchers, separated by space and time but united by the desire to improve the lives of people. Pomposity might be expected in a lecture room but is very ridiculous in a committee room.

Serious economists will be thoroughly committed to seeking truth from their own approach. But entirely aware of the partiality of their approach, they will converse with other students of human nature and learn from them (and teach them). They will abstract heroically from irrelevant aspects, and heroically proxy the neglected factor the next time around. They will pursue and teach truth without any regard to its practical use, but keeping the practical end in mind all the while. They will develop rules and consider exceptions. They will use a priori theorizing and data-driven empiricism. They will abjure ideology and embrace it. They will be committed scientists and smirk at their own scientific pretentions. They will be, well, two-handed.