After her contribution to the pamphlet with Norman Daniel, the earliest of Anscombe’s published writings is from 1948, based on a debate she had with C. S. Lewis, who was then a fellow at Magdalen College, Oxford. The debate took place in Oxford’s Socratic Club, and concerned the third chapter of Lewis’s book Miracles, which argues that human thought cannot be relied on “if it can be fully explained as the result of irrational causes.” This argument was supposed to show that the only way to have a reasonable belief in the reliability of human reason is to believe in a supernatural God.

Anscombe criticized Lewis’s argument, claiming that it was based “on a confusion between the concepts of cause and reason.” In evaluating, for example, the quality of the argument in a piece of writing, our concern with whether it expresses good reasoning is not about “the circumstances of its production,” but rather about whether the evidence it offers is sufficient to prove its conclusion. She also argued that the term “explanation” can encompass many different things, and that a causal explanation of human thought and behavior in terms of regular patterns in the universe would not preclude there also being explanations in terms of the reasons why people act and believe as they do. Both of these arguments likely had their roots in Anscombe’s interactions with Wittgenstein, as they mirrored ideas that were central to his Philosophical Investigations, and that Anscombe would develop in her own work of the following decade.

There was for some time a lot of controversy over how Lewis was affected by this episode. Anscombe wrote to Wittgenstein the day after the debate that Lewis had been “much more decent in discussion than I expected, though he was glib and played all sorts of tricks to obscure the issue.” She did add, however, that during the discussion the secretary of the club “started going for Lewis, who had said something about having written the book ‘at a fairly popular level’—he [the secretary] reproached him almost in moral terms, that one should not, for the sake of popularizing, put up a bad argument.” While several of Lewis’s biographers claimed that the debate humiliated him and was the end of his career as a public intellectual, Anscombe later wrote that those who knew Lewis reported no such thing at the time, and noted that Lewis revised the argument of that chapter for the second edition of Miracles, presenting it in a way that she found more appropriate “to the actual depth and difficulty of the question being discussed.”

The closing paragraphs of Anscombe’s pamphlet “Mr. Truman’s Degree” raised the question of “why so many Oxford people are willing to flatter” a man who had approved the massacre of entire cities. “I get some small light on this subject,” Anscombe wrote, “when I consider the productions of Oxford moral philosophy since the First World War, which I have lately had occasion to read.” (While her early research interests had been in metaphysics and the philosophy of mind, it was when her Somerville colleague Philippa Foot spent a year visiting in America that Anscombe began reading modern ethicists in order to take over Foot’s course in moral philosophy.) One important strand that Anscombe identified in these philosophers was “a doctrine that it is impossible to have any quite general moral laws.” According to this doctrine:

[S]uch laws as “It is wrong to lie” or “Never commit sodomy” are rules of thumb which an experienced person knows when to break. Further, both his selection of these as the rules on which to proceed, and his tactful adjustments of them in particular cases, are based on their fitting together with the “way of life” which is his preference.… These philosophies, then, contain a repudiation of the idea that any class of actions, such as murder, may be absolutely excluded.

This, again, is what Anscombe would call the consequentialist doctrine that any type of action can in principle be justified by considering its likely consequences. According to this logic, it was because his action ended up saving lives, by bringing an earlier end to the war, that Truman was justified in massacring the citizens of Hiroshima and Nagasaki.

In “Modern Moral Philosophy,” the influential 1958 paper in which she introduced the term “consequentialism,” Anscombe went to greater length in identifying the error that her Oxford colleagues had committed. This followed a BBC radio address given about a year earlier, in which Anscombe had posed the question “Does Oxford moral philosophy corrupt youth?” and answered it in the negative: the youth were not corrupted, she said, since these philosophers only taught the bad moral views that young people held anyway. Anscombe’s 1958 paper began with a whirlwind history in which she dismissed a series of moral philosophers from David Hume (“sophistical”) to Immanuel Kant (“useless”) to John Stuart Mill (“stupid”) to Henry Sidgwick (“dull” and “vulgar”), and then took aim at the “shallow,” “provincial,” and “corrupt” work of her contemporaries. The latter criticism centered on a conception of intentional action that Anscombe located in the work of Sidgwick, according to which a person “must be said to intend any foreseen consequences of [their] voluntary action.” On Anscombe’s reading, Sidgwick used this definition “to put forward an ethical thesis which would now be accepted by many people: the thesis that it does not make any difference to a man’s responsibility for something that he foresaw, that he felt no desire for it, either as an end or as a means to an end.”

Anscombe illustrated the upshot of this thesis with a simple example. According to a view like Sidgwick’s, there is no difference between the responsibility a man has for withdrawing material support from his children if he does this in order to achieve some further end, and the responsibility the same man would have if he was imprisoned for refusing to commit a disgraceful act. In both cases the man foresees that his choice will have the consequence of withdrawing material support from his children. Therefore, according to Sidgwick’s view, in each case the man is responsible in the same way for this outcome.

It is straightforward to extend this analysis to Truman’s decision to bomb the Japanese cities. Truman could foresee that his decision would lead to the deaths of thousands of innocent civilians. Yet, his defenders claim, a similar or greater number of civilians would have been killed had he chosen not to drop the bombs. On this analysis, Truman would have been equally responsible for the civilian deaths in either case. So the only thing that matters is whether he made the choice that led to better consequences overall—that is, to fewer total deaths.

Anscombe noted in “Modern Moral Philosophy” how surprising it was that none of the philosophers who accepted this position displayed any awareness of how their conclusions were “quite incompatible with the Hebrew–Christian ethic.” According to this ethic, she wrote, “there are certain things forbidden whatever consequences threaten,” and faced with the possibility of doing these things “you are not to be tempted by fear or hope of consequences.” But she saw that in her context she could not respond to this situation simply by defending traditional moral absolutes. Instead, the way forward was to begin “by banishing ethics totally from our minds,” in order to consider “simply as part of the philosophy of psychology” the concepts that ethical thinking presupposes. Among these she listed “action,” “intention,” and “wanting”—all of which are explored at length in the short book she had published a year earlier under the simple title Intention.

Anscombe’s Intention is an extraordinarily dense and difficult book, even by the standards of contemporary philosophy. It is just ninety-four pages long, comprising fifty-two numbered sections that range in length from a single paragraph to four or five pages. In this space the book treats an exhausting range of topics—and yet it has no obvious structure, no theses introduced at the beginning or stated clearly at the end, and barely any reference to the authors whose work it engages. It baffled several reviewers when it first appeared, and for a while went out of print. Yet when Harvard University Press reissued Anscombe’s book in 2001, the following quotation from the philosopher Donald Davidson appeared on the cover: “Anscombe’s Intention is the most important treatment of action since Aristotle.”

Anscombe would likely have objected that such praise overlooked at least the importance of Thomas Aquinas, whose influence is everywhere in Intention, even though his name appears only in one stray footnote. Anscombe’s daughter, Mary Geach, wrote in 2011 that her mother “drew on [Aquinas’s] thought to an unknowable extent: she said to me that it aroused prejudice in people to tell them that a thought came from him: to my sister she said that to ascribe a thought to him made people boringly ignore the philosophical interest of it, whether they were for Aquinas or against him.” Because of this, rather than repeating Aquinas’s theses and rehearsing his arguments for them—an approach entirely out of keeping with the way Aquinas himself built on the work of philosophers like Aristotle and St. Augustine—Anscombe’s writing appropriates Aquinas’s ideas in a fresh and novel guise, free of scholastic terminology and ready to be engaged by the contemporary reader.

Because of its scope and style, Intention resists easy summary. Anscombe is opposed throughout the book to thinking of intention primarily as a matter of one’s internal psychology—as the objective one has in doing a certain thing, or the willingness to do a thing on a certain occasion. At one point she identifies Wittgenstein as having advanced such a view in his Tractatus: “The world is independent of my will,” Wittgenstein wrote, and so action depends on a “presumed physical connexion” between one’s will and one’s bodily movements. In a notebook that likely dates from the 1950s, Anscombe cited this passage and wrote of feeling “more certain that there is a mistake here than about anything else in the Tractatus.” She continued: “I wish to say that ‘I do what happens’ when I act. The extraordinary thing is that this assumes an air of paradox.” This quoted remark reappeared in the text of Intention, where Anscombe wrote that though “everyone who heard this formula found it extremely paradoxical,” in fact it can be shown to make good sense.

In order to save this remark from paradox, Anscombe argued in her book that we use the concept of intention to describe what happens in most of our ordinary ways of describing human life. Imagine, for example, that you come into Anscombe’s study and find her sitting at her desk, with a pen in her hand that she is moving across the page. What is she doing? Writing, you will answer—and in describing her movements in this way you have already gone beyond a description in terms of physical bodies and forces. Mere physical objects can shatter, rise, and roll down hills, but they cannot write, jump, or walk. To describe a movement with words like these is to describe it as the execution of an intention.

How does this account apply to the case of Truman? The analysis of intention that Anscombe rejected holds that since Truman did not want the citizens of Hiroshima and Nagasaki to die—since their deaths were not part of his ultimate objective—they therefore fall outside the scope of his intention. By contrast, Anscombe argues that any sensible description of what Truman did must include the fact that he used these civilian deaths as a means to his end. These deaths were not merely incidental, since it was by killing the civilians that Truman brought the war to a close. Truman had innocent people killed in order to achieve his aims—and to do such a thing is to commit an act of murder.