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27

First Steps in Lojban

Lesson 27. (Extra) Propositions, properties, relations

Koshon
Koshon

Welcome to the "Back Alley"! This is a little philosophy and logic gym tucked away next to the main Lojban course. It's totally optional, but it's a lot of fun if you like to think about how language and thought fit together.

Propositions

Sentences in different languages can often mean exactly the same thing, even if they use completely different words ("I am a human," .i mi remna, Mi estas homo, etc.). We call that shared underlying meaning a proposition. In Lojban, any declarative sentence that expresses this meaning is a propositional sentence.

The word du'u is used to wrap a whole sentence into a single item: "the proposition that [sentence] is true."

du'u [sentence]
The proposition expressed by the given [sentence]. (x1 is the proposition, x2 is its textual representation).

Philosophers like to argue about what a proposition "actually" is—is it an idea, a set of possible worlds, or a disposition to behave in a certain way? For our purposes in Lojban, you can just think of it as the "logical content of a declarative sentence."

ce'u — open place in a property

Wait, ce'u remna isn't a complete sentence by itself. It's more like a property ("to be human"), with a "blank space" or "slot" marked by the word ce'u. (Most introductory texts and the CLL discuss how this connects to ka abstractions—check those out if you want to dive deeper!)

Exercises

  • Try building a du'u-sentence that pairs the same proposition across two different languages using those zoi quotation markers we learned in Lesson 22.
  • How would you say "the English version of the proposition is identical to the Japanese version" using our identity word du (from Lesson 15)?

Relatives refresh

ti noi ke'a remna ku'o cu melbi "This thing—which, as it happens, is human—is beautiful."

Try connecting these abstract properties to what you've learned about poi and noi relative clauses.

True or false

Pick whether each statement is true or false according to the lesson.

  1. A ka clause always contains at least one ce'u.

  2. In Lojban, properties vs relations differ by whether the underlying predication has one open slot or more.

  3. A proposition is the meaning/content of a sentence; what that meaning “really is” can be debated.

  4. ce'u is a free variable, while mi, ta, zo'e, and lo broda are bound or filled arguments.