Do the poor lack free will? I ask because of a Twitter argument I've had with Peter Risdon. I said that in criticizing the poor for their junk food diet, Jamie Oliver was blaming the victim. Peter replied: "You think that being poor removes from individuals the ability to decide how to act, albeit within limits affected by poverty?"

I'll not go as far as "removes." But I would stress the many channels in which the poor's agency to act "well" is constrained. These include:

- Poverty limits options. If you're poor, you're more likely to live in a food desert where healthy eating is less feasible. Sure, you could get nutritious food cheaply or even for free if you look in the right places. But to believe this is true for all the poor is to commit the fallacy of composition. And of course, this is only one of many ways in which poverty limits freedom; not least of the others is that poverty is associated with poor education.

- Social roles, priming and stereotype threat. The famous Stanford prison experiment showed how people quickly come to take on social roles, even if these are randomly assigned: guards became belligerent and prisoners docile. "Most of us can undergo significant character transformations when we are caught up in the crucible of social forces." writes Philip Zimbardo.People live up or down to stereotypes, especially if they are reminded of them. So if the poor are told that they are mindless, low-achieving criminals, they'll act the part.

- Learned helplessness and adaptive preferences. If people are told (for generations) by teachers, rulers and bosses to "do as your told" many will eventually become passive, and unaware of what agency they have. And if they have few attractive job opportunities, some will resign themselves to that, and become "lazy."

- Bad incentives. What's the point of getting a job if you lose benefits and face high costs of travelling and childcare? What's the point of doing well at school if you'll face social isolation (not just a problem for blacks)? Why save if you'll only be robbed?

- Role models. If you see people like yourself doing something, you'll think "I can do that". This is one reason why we often follow our parents' career paths; Jamie Oliver's parents ran a pub, and it's a small step from there to a career in cooking. If, though, you lack such models, you'll be less aware of your options.

- Peer effects. It's increasingly well known that our peers shape our choices. If our mates go to university, we're likely to. If they become criminals, so are we.

Now, in saying all this I'm not wholly denying that the poor have free will. It's just that it is a damned sight harder for them to choose well than it is for people in more favourable circumstances.

Nor is it only the poor who are constrained. There's not much agency involved when an Etonian goes to Oxford and thence to politics or the City: As Owen Jones rightly wrote, David Cameron is also "a prisoner of his background." Marx was aware that capitalists' choices are constrained by the forces of competition. And capitalists are themselves quick to deny their own agency when they claim that job cuts or austerity are "necessary."

Agency, in any fullish sense of the word, requires particular conditions which are only rarely met. What robs the poor of dignity - to use Peter's phrase - is not my pointing out the degree to which they lack free will, but rather the existence of those social conditions that limit it.