At one point in Episode 34 (around 79:10), I made a mistake. Oops. Might as well set it right on the blog!
We were talking about Bertrand Russell's classic 1905 article, 'On Denoting.' Russell is trying to do many different things in that article. But for now, we only need to concern ourselves with one in particular, which is that he wants to give an accurate account of what sentences with words that fail to refer mean.
OK; so what's all this stuff about referring and failing to refer? The basic idea here is that words typically stand for things. The name 'Matt' refers to me, and the noun phrase 'the Grand Canyon' refers to the grand canyon, and the phrase 'Rowan Atkinson's favorite car' stands for Rowan Atkinson's favorite car.
Now, you might think that words always referred to things. And in most ordinary situations, they do. But upon further reflection, it turns out that sometimes, when we make mistakes, a word can fail to refer to anything. For instance, imagine that I see two people walk into a party: a friend of mine, and someone who I mistakenly take to be her sister. Furthermore, imagine that this friend of mine doesn't even have a sister. In that scenario, if I said 'Can I get your sister anything to drink?' then my friend would be quite confused. Why? Well, because one of the noun phrases I was trying to use was messed up. Specifically, the noun phrase 'your sister' would fail to refer to anything.
Russell was interested in whether sentences with noun phrases that failed to refer could be true or false. Suppose this time that instead of asking my friend whether I could get her sister anything to drink I made a statement. Something like: 'Your sister must be tired.' Now, is that statement true or is it false? It obviously isn't true. But whether it's false is kind of a trickier question.
There was actually a big debate about this. Here's a reason for thinking that 'Your sister looks lovely tonight' isn't false either. If I asked my friend whether her sister was tired, she wouldn't say 'yes,' because that would imply that she had a sister. But she wouldn't say 'no,' because that would also imply that she had a sister. Denying that her sister is tired suggests that she has a sister, only that that sister of hers isn't tired. So it seems as though the correct answer to 'Is your sister tired?' is neither yes nor no. This is what led certain philosophers (such as Frege) to conclude that sentences like 'Your sister must be tired' (said to someone who doesn't have a sister) are neither true nor false.
Russell disagrees with Frege here. He thinks that sentences like 'Your sister must be tired' (said to someone who doesn't have a sister) must be false. One reason he gives for thinking they're false is that Frege's theory makes incorrect predictions about what atheists are saying. If the atheists were correct that God didn't exist, and Frege was correct that sentences with noun phrases that failed to refer were neither true nor false, then 'God is all powerful' would have to be neither true nor false. But an atheist would never claim that statements like 'God is all powerful' were neither true nor false. The whole point of atheism is to say that they're false. Or so Russell argues.
Anyway, let's get back to the correction. At this point in the discussion, the four of us were talking about Russell's view to the effect that sentences with non-referring expressions in them are false (rather than neither true nor false). And I momentarily mixed up what Russell has to say about 'Your sister is tired' and what Russell has to say about 'Your sister isn't tired.' In the podcast, I said that he thinks the former sentence is ambiguous. But actually, he thinks the former sentence is just false, for the reasons given above. It's the latter sentence that he thinks is ambiguous. We don't really have to get into why right now, since there may be an episode on Russell in the future. But basically, Russell's semantic theory commits him to thinking that whenever you have a sentence that contains both the word 'not' and a noun phrase (like 'your sister), then it can have two possible interpretations:
i) There is a person who is your sister and who is not tired.
ii) There is no person who is your sister and who is tired.
But since 'Your sister is tired' doesn't have the word 'not' in it, it only has one possible interpretation. And on that interpretation (when it's said to someone who doesn't have a sister), Russell thinks it is false.