Are you sure you understand what people say? Unfortunately, you cannot be certain.
Everyone is Sherlock Holmes
There are several schools of thought in language comprehension. Perhaps the most common is those who think language is inferential. What that means is that you understand meaning based on the entire wider context and associations. You then make a series of deduction about what someone meant (although you might make these deductions unconsciously)
'after the plane crash, the authorities needed to find a place to bury the survivors'
You likely understood what that meant, despite the fact that survivors should be replaced with a word like deceased or dead. Although it is possible that the authorities wanted to bury the survivors, you made the deduction that it was more likely that the authorities wanted to bury the dead.
Skepticism and all that
Some people aren't happy with this answer. This is in part because someone might mean any number of things which are compatible with your deductions.
Conditional probability (optional)
If you want to be formal about this [optional section], the first approach requires your brain creating some sort of 'probability distribution' of what is likely. A probability distribution simply models how likely different outcomes are. If you are going to make a probabilistic judgement based on some evidence, you need to be able to have a way of assigning probabilities to the evidence.
Further, your brain seems to use conditional (or Bayesian) probability with this approach. It has a 'distribution' for the meanings of a word and how likely it is to be used in a certain way. For instance, if I say the word 'red' you get a sense of what its possible meanings are. Given the overall shape of the sentence and the other words, it then adjusts what it is most likely to mean. If say 'I hit him, and he saw red' I am referring to 'seeing red', i.e. that he was angry. It is possible he just saw something red, but given I hit him, this is unlikely. Instead, if I say 'I thought the paint was pink, but he saw red' this is (probably) referring to him seeing the colour red, not getting angry.
Turtles all the way down
Unfortunately [non technical again!], to make a judgement about whether something is likely requires some previous information. This makes the entire enterprise circular. For instance, if I saw rain on the window, I assume it is raining because I have experience which confirms this. You might go outside one day and get wet after seeing rain on the window.
If my only evidence was that I saw it raining on the window yesterday, and the day before (and so on) then I have no evidence. I would be deducing that it was raining outside because I deduced yesterday it was raining outside! Perhaps it was just a piece of gardening equipment which watered the grass, or a leaky pipe?
Similarly, we would have to actually understand what someone said once to begin creating a valid probability distribution (along with some other assumptions).
With the first approach we are left with no firm reason for knowing someone said what we think they said. And this is sad.
One response which has been floated. The idea is that meaning is intrinsic in the sounds you hear (and words).
This faces its own problems:
Even if it does have intrinsic meaning for me in the sounds, then how do you know that it has the same intrinsic sounds for others? This fails to deal with the skeptical issue. For example, someone might train your dog to make sounds similar to 'I love you'. This may have intrinsic meaning for you in the sounds which it doesn't for the dog.
Philosophy as word games
The very fact that Philosophers write about this shows their assumptions that people can somewhat understand.
Is this just another axiom, or to we to some extent understand what others are saying intuitively? Maybe a baby's wail can convey intrinsic information about both sides?
We might say:
- If the wail came from a baby (as opposed to some robot or similar) then we gain valid information about the state of that baby.
I.e, under milder assumptions over the nature of what type of being is making the utterance, it is possible that the intrinsic meaning approach does work.