George and Ringo both have $6000 in their bank accounts. They both are thinking about buying a new computer, which would cost $2000. Both of them also have rent due tomorrow, and they won’t get any more money before then. George lives in New York, so his rent is $5000. Ringo lives in Syracuse, so his rent is $1000. Clearly, (1) and (2) are true.

(1) Ringo has enough money to buy the computer.
(2) Ringo can afford the computer.

And I think (3) is true as well, though (4) is less clearly true.

(3) George has enough money to buy the computer.
(4) George can afford the computer.

But I want to focus for now on (3). It is a bad idea for George to buy the computer; he won’t be able to pay his rent. But he has enough money to do so; the computer costs $2000, and he has $6000 in the bank. So (3) is true. Admittedly there are things close to (3) that aren’t true. He hasn’t got enough money to buy the computer and pay his rent. You might say that he hasn’t got enough money to buy the computer given his other financial obligations. But none of this undermines (3).

The point of this little story is to respond to an argument Michael Blome-Tillmann makes in “a paper”:http://users.ox.ac.uk/~quee1101/papers/mbt_mate.pdf attacking interest-relative invariantism (IRI). (He calls IRI ‘SSI’, which I think is unfortunate, since everyone agrees that knowledge is subject-sensitive. No one thinks S knows that p entails T knows that p.) Here is one of the arguments he makes.

Suppose that John and Paul have exactly the same evidence, while John is in a low-stakes situation towards _p_ and Paul in a high-stakes situation towards _p_. Bearing in mind that SSI is the view that whether one knows _p_ depends on one’s practical situation, SSI entails that one can truly assert:

(11) John and Paul have exactly the same evidence for _p_, but only John has enough evidence to know p, Paul doesn’t.

And this is meant to be a problem, because (11) is intuitively false.

But SSI doesn’t entail any such thing. Paul does have enough evidence to know that _p_, just like George has enough money to buy the computer. Paul can’t know that _p_, just like George can’t buy the computer, because of their practical situations. But that doesn’t mean he doesn’t have enough evidence to know it. So there isn’t a problem for SSI here.

In a footnote attached to this, Blome-Tillmann tries to reformulate the argument.

I take it that having enough evidence to ‘know _p_’ in _C_ just means having evidence such that one is in a position to ‘know _p_’ in _C_, rather than having evidence such that one ‘knows p‘. Thus, another way to formulate (11) would be as follows: ‘John and Paul have exactly the same evidence for _p_, but only John is in a position to know _p_, Paul isn’t.’

The ‘reformulation’ is obviously bad, since having enough evidence to know _p_ isn’t the same as being in a position to know it, any more than having enough money to buy the computer puts George in a position to buy it. But might there be a different problem for SSI here?

No; the reformulated argument isn’t a problem because the conclusion is not unacceptable. Indeed, the conclusion is a kind of conjunction that is made true all the time, on relatively uncontentious theories of evidence. Consider this example.

Mick and Keith both have evidence _E_, which is strong inductive evidence for _p_. And _p_ in fact is true, just as _E_ would suggest. If Keith were to conclude _p_ on the basis of _E_, that would be knowledge. But Mick has been taking some philosophy classes. And as luck would have it, he has been taking classes from a smart Popperian, who has convinced him that induction is not a source of knowledge. Now if Mick concluded _p_ on the basis of _E_, this would not be knowledge, because his Popperian beliefs would constitute a doxastic defeater. So Mick and Keith have exactly the same evidence for _p_, but only Keith is in a position to know _p_, Mick isn’t.

I think it’s interesting to think about ‘afford’ in this context, since it seems very likely that some kind of IRI analysis of ‘afford’ will be true. We don’t want to have any kind of contextualism about ‘afford’, at least nothing like modern day epistemic contextualism. It would be crazy to say that if _my_ rent is $5000, and it is due tomorrow, then (2) is false, because after all, in my context someone with Ringo’s money couldn’t buy the computer and meet their financial obligations. If I’m right that ‘afford’ is interest-relative, then looking at the way ‘afford’ patterns should provide some useful evidence for or against IRI.