So let’s talk about clues. You might think that people say what they
mean, but a big part of what’s actually being said is nowhere to be found in the words
themselves. Sentences are like a crime scene without witnesses:
nobody saw what happened, but the words that were left behind give you everything that you need
to solve the mystery of meaning. The good news is, if you already speak a language, you’re
a veritable Sherlock Holmes. I’m Moti Lieberman, and this is The Ling Space.
So we’ve talked about pragmatics before, the study of how language is used in context,
and the assumptions that we make to understand each other.
We all follow the Cooperative Principle, which is a number of maxims that describe
how to be nice and considerate conversation partners. There are four basic rules that
we follow, and that we assume that other speakers follow all of the time: the Maxims
of Quality, Quantity, Relevance, and Manner.
So, if I tell you that “during John and Mary’s wedding, Sherlock noticed three signs”,
you’re probably going to assume that I’m following the Maxim of Quantity and being as
informative as I can be, meaning that he saw exactly three. I never said “exactly”,
but being the detective that you are, you figured out that that’s exactly what I meant.
But if you were just a Logic-Bot, interpreting everything that you hear as the absolute
logical truth? You wouldn’t be clever enough to pick this up.
Straight-up logic isn’t programmed to be cooperative, and so this sentence would be
true even if Sherlock had seen four signs! Or five! To Logic-Bot 3000, the original sentence
isn't wrong; it’s just kind of... incomplete.
Now, a conclusion that we draw from incomplete information, like the number of signs
being exactly three, is called an implicature.
And because implicatures are really just deductions, and not facts, that means it’s
possible for them to be wrong! But the thing is, even if the implicature
were false, the original sentence still stays true, as long as there were at least three signs.
This is a defining property of how facts and languages interact, and it’s called “cancellability”.
So, let’s say John asked Martha for some biscuits, and she said “I’m not your
housekeeper”. Logic-Bot would have a hard time getting this, because
it doesn’t really seem like one sentence really has much to do with the other.
But because we figure that speakers obey the Maxim of Relevance, and tend to say things
that make sense, we figure that she’s saying no, and is probably annoyed, to boot.
That’s the implicature. But the evidence is always circumstantial; it’s possible
that she just misheard John, and that her response has nothing at all to do with what
he actually said. In this case, we would just have a simple misunderstanding,
and the implicature would turn out to be wrong. But that doesn’t make the statement that
she’s not his housekeeper false.
It’s important to note that just because we can cancel implicatures doesn’t mean
that we usually treat them so callously. People will often reject a sentence as being
untrue if it’s only logically true, but pragmatically bad.
So look at an experiment like this 2003 study. Researchers presented participants with a
number of scenarios like having every single horse in a scene jump over a fallen tree.
Then they asked whether “Some of the horses leapt over the log” made for a good description.
Adults rejected over 92% of the inappropriate implicatures, even if they were logically
true. We really do care about these things. So, implicatures will usually point you in
the right direction, but they can sometimes be misleading.
Thankfully, words can leave behind fingerprints too, which brings us to Exhibit B: entailment.
If I told you that Martha made a pot of tea, you would know for sure that she put the
kettle on. This is because you understand that you can’t
make tea without putting the kettle on; even Logic-Bot knows this! This means that the first
sentence entails the second one. There’s no way for the first sentence to be true while
the second sentence is false; the truth of the first sentence guarantees the truth of the
second one, even if the second sentence remains unsaid.
And this is the kind of thing that Logic-Bot 3000 totally gets. Now, there’s lots of
ways for one sentence to entail another.
For example, we could swap a phrase in a sentence with its synonym, so that “Greg works at
Scotland Yard” entails “Greg is employed at Scotland Yard”, and vice versa!
Another way to get at entailment is to replace a specific thing with something more general.
In this way, “Irene is a woman” entails “Irene is a person”. Or, we could use
what we know about the world, so that “The scientist that knows Sherlock’s secret got
engaged” entails “Molly Hooper got engaged”.
Finally, we can play around with the structure of our sentences to arrive at entailment.
By stripping away extra material, we can get from “Sally and Philip disliked the detective”
to “Philip disliked the detective”. Or “Sherlock figured out the password on
the third try” to entail “Sherlock figured out the password”.
The thing that all these different kinds of entailment have in common is that, unlike
implicatures, they’re not cancellable.
There’s no way that he would have figured out the password on the third try if he never
figured it out at all. It’s a contradiction that just doesn’t make sense! When it comes
to entailment, the truth is always guaranteed. Now, you might be thinking that this case
is closed, but we haven’t even tracked down our biggest lead yet: the smoking gun of presupposition.
Take the following sentence: “John listened as Sherlock played the violin”.
We know that if this sentence is true, it must be true that Sherlock was playing the violin;
after all, how could John hear something that didn’t even happen? So the first sentence presupposes
the second one. But what’s really amazing about this is
that even if we turn the sentence around, and make it “John didn’t listen as Sherlock
played the violin”, we still know that Sherlock must have been
playing music.
Presupposition is so resilient, it even survives negation! That doesn’t happen with entailment.
If you wanted to claim that Martha didn’t make a pot of tea, that doesn't tell you anything at all
about whether she put the kettle on. The entailment is broken.
But presupposition is like entailment on steroids. In fact, it can even be a little too much for
Logic-Bot to handle.
If we asked “Logic-Bot: is it true that Sherlock’s sister is a detective too?”,
his poor robot head might explode What we did was sneak a false presupposition
into the question. Sherlock doesn’t even have a sister, so it can’t be
true that she’s a detective; weirdly, it can’t really be false, either, because that
would mean he had a sister that does something other than detective work. Logic-Bot just
can’t deal with sentences that are neither true nor false; it’s a bit of a paradox!
So like entailment, presuppositions aren’t cancellable. If we try to deny it, the truth
of the sentence becomes impossible to judge. And like entailment, there are a few different ways
to trigger presupposition. One is to use the definite article: so, the word “the”.
If I say “Sherlock suspects the taxi driver”, that pretty much means that there has to be a taxi
driver somewhere out there for it to make any kind of sense; the sentence presupposes a world
in which a taxi driver exists.
Another way is with certain kinds of verbs, like when I say “The suspect admitted to
using poison”, he better have actually used some! Otherwise, the presupposition ends up
being false, and it’s hard to know exactly what it could mean. Certain adverbs trigger
presuppositions, too, like the word “again”. If “Moriarty appeared again”, he must
have appeared at least once before. If he hadn’t, the original sentence just becomes nonsense.
Presupposition, together with the various flavours of entailment and implicature that
we’ve discussed here, make up all the different kinds of extra information that our sentences carry.
This isn't the kind of stuff that you can see with the naked eye, but with careful investigation, it becomes
elementary: when we speak, we communicate so much more than just the words that we say.
And luckily, because we aren’t simple robots, we can read the clues people drop to put together
a compelling case.
So, we’ve reached the end of The Ling Space for this week.
If you managed to see the investigation through to the end, you learned that implicatures
are deductions that we make about what a speaker actually means, based on the assumption
they’re being cooperative; that implicatures are cancellable because
they can turn out to be false;
that an entailment means if a sentence is true, another related sentence will also
be true; and that sentences with presuppositions require that some background information already
be established, and they can even survive negation!
The Ling Space is produced by me, Moti Lieberman, and directed by Adèle-Elise Prévost. This
week’s episode was written by Stephan Hurtubise. Our editor is Georges Coulombe, our music
and sound design is by Shane Turner, and our graphics team is atelierMUSE. We’re down
in the comments below, or you can bring the discussion back over to our website, where
we have some extra material on this topic.
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personal Ling Space, please subscribe. And we’ll see you next Wednesday. Phir milenge!