Your vocabulary literally changes the universe.
''Perhaps the most different counting system from that of modern Western civilisation is the “one-two-many” system used by the Pirahã people. In this system, quantities larger than two are referred to simply as “many”. In larger quantities, “one” can also mean a small amount and “many” a larger amount. Research was conducted in the Pirahã culture using various matching tasks. These are non-linguistic tasks that were analyzed to see if their counting system or more importantly their language affected their cognitive abilities. The results showed that they perform quite differently from, for example, an English speaking person who has a language with words for numbers more than two. For example, they were able to represent numbers 1 and 2 accurately using their fingers but as the quantities grew larger (up to 10), their accuracy diminished. This phenomenon is also called the “analog estimation”, as numbers get bigger the estimation grows [1] Their declined performance is an example of how a language can affect thought and great evidence to support the Sapir-Whorf Hypothesis.
Orientation
Language also seems to shape how people from different cultures orient themselves in space. For instance, people from an Aboriginal community called Pormpuraaw define space relative to the observer. Instead of referring to location in terms like “left”, “right”, “back” and “forward”, most Aboriginal groups, such as the Kuuk Thaayorre, use cardinal-direction terms – north, south, east and west. For example, speakers from such cultures would say “There is a spider on your northeast leg” or “Pass the ball to the south southwest”. In fact, instead of “hello”, the greeting in such cultures is “Where are you going?” and sometimes even “Where are you coming from?” Such greeting would be followed by a directional answer “To the northeast in the middle distance”. The consequence of using such language is that the speakers need to be constantly oriented in space, or they would not be able to express themselves properly, or even get past a greeting. Speakers of such languages that rely on absolute reference frames have a much greater navigational ability and spatial knowledge compared to speakers of languages that use relative reference frames (such as English). In comparison with English users, speakers of languages such as Kuuk Thaayorre are also much better at staying oriented even in unfamiliar spaces – and it is in fact their language that enables them to do this.[2]''
Edit: I realise that I foolishly over-complicated and worded my question in a way that obscured what I actually meant. In essence, my question was: if we didn't have specialised vocabulary for things - say, in the area of rationality - would our rationality be hampered by our inability to be specific without long-windedness? Often words are created to bridge this gap when new concepts are created, so if we didn't have those words, would it take longer for us to understand or communicate and idea (to others or ourselves) and make it more difficult to be rational?
From the direction of the comments the general answer to my initial question is coming across as: "words are useful for communicating explicitly, and so an extensive or highly specialised vocabulary can be useful, if and only if the person/people with whom you are communicating understands those words". The internal understanding of concepts does not need words and thus a vocabulary.
I am curious about the relevance of vocabulary to rationality. I'm not talking about a basic vocabulary, but a vocabulary beyond that of the average, English-as-a-first-language adult. I believe there are a few correlations between intelligence as measured by IQ and vocabulary, as well as vocabulary and income(via IQ), but anecdotally I think it's fair to say that there are certainly people who are highly intelligent, but often irrational.
In reading through LW, I've come across a lot of new terms specific to certain areas of study, and I've had to look them up to fully understand that discussion of rationality - I assume this is probably true of most people new to the field, and applies to most specialised fields. Jargon is obviously useful within given fields where there is a need for detailed discussion of highly specialised topics, and helps one to discuss that area, but is it necessary to understand that jargon in order to practice in the field?
For example, I would think that a general practitioner would have trouble within his field if he did not hold the language to be able to specify what, in particular, was wrong with a patient, even if he knew what it was. Or could he not even be able to understand, say, that a patient was having a heart attack if he did not have the words for it? I suppose history might be a good indicator of this, or new scientific phenomena.
The field of rationality is one of both practice and theory - but if we didn't have an advanced vocabulary, could we still be highly rational? For example, my stepfather didn't finish high school, and makes up words like "obstropolous" (which I think kind of means stubborn and difficult to deal with on purpose) to say what he means, but he's also the type of person who, in a emergency, takes the most logical, rational course of action without panicking or doing something silly. On the flip side of this, he makes grand generalisations about races, religions and people while refusing to discuss the possibilities of individuality, or conceding any part of his argument to, well, evidence.
So do you have an argument for or against the need for an advanced or specialised vocabulary to be rational? Is it a question that's too vague, or with too variable an answer? I couldn't find any scientific papers on rationality and vocabulary, so I don't know if there's any data for or against, but I think it's an interesting question.
(This is my first LW article, so please be gentle but thorough with any criticisms you may have - I'm happy to improve or clarify!)