Elizabeth Anscombe was a hugely important 20th-century philosopher who worked on many topics, including history, metaphysics, religion, and language. But above all she was a pioneering figure in the philosophy of action, where she put forward fascinating theories about intention.

To get a feel for one of those theories, imagine you’re on a train with three other passengers, all strangers. When the train leaves the station there’s a sudden jolt, and Passenger A bumps into you; he makes his apologies, and all is fine. When the train’s in steady movement, Passenger B bumps into you on purpose. (This fellow's probably thinking to himself something along the lines of “that guy looks like a literature professor! I’ll teach him not to talk about Proust all the time.”) This is clearly a different case.

Somehow you make it to your destination without further damage. At this point, Passenger C, who's in a hurry to get to an interview, makes a bolt for the door—and bumps into you on the way. (You're really not having a great day, are you?) OK, so Passenger A had no intention to harm you; Passenger B jostled you on purpose; but what should we say about Passenger C? Maybe it's simple: she moved her body through space, in a particular trajectory; that trajectory collided with your body; and she followed that trajectory deliberately—so she deliberately ran into you. But somehow that doesn't feel right.

Here’s where Anscombe has a really interesting insight: she says there are many ways of describing one and the same action, and whether or not someone did something intentionally depends on how we describe it.

Anscombe's most famous example starts with a guy putting water into a well, from where it goes into a house. This guy may sound like a helpful sort, but hold on: it turns out that the water is poisoned. At which point he may sound like a villain, but hold on again: the people in the house are Nazis!

Confused? Well, Anscombe’s point is that we can describe what this man is doing in four different ways: (a) he’s putting water in a well; (b) he’s supplying water to the house; (c) he’s poisoning people; (d) he’s killing Nazis. Depending on which description we use, we're going to assess his action differently.

So what does this tell us about the woman in the train? She also did something that can be seen in many different ways: she ran toward a door; she rushed to get to her interview; she bumped into a literature professor. Her action looks very different depending on how you describe it.

More specifically, she only intended some of this—she certainly never meant to spoil anyone's day. According to Anscombe, she didn't even intend to get the job she was interviewing for: you can’t intend to get a cool job, since getting a job depends on other people and so isn’t entirely up to you.

So where does that leave us? In the capable hands of our Anscombe-expert guest, Rachael Wiseman, author of The Routledge Guidebook to Anscombe’s 'Intention'.