Predicate words, called brivla , are at the core of Lojban. They carry most of the semantic information in the language. They serve as the equivalent of English nouns, verbs, adjectives, and adverbs, all in a single part of speech.
Every brivla belongs to one of three major subtypes. These subtypes are defined by the form, or morphology, of the word – all words of a particular structure can be assigned by sight or sound to a particular type (cmavo, brivla, or cmevla) and subtype. Knowing the type and subtype then gives you, the reader or listener, significant clues to the meaning and the origin of the word, even if you have never heard the word before.
The same principle allows you, when speaking or writing, to invent new brivla for new concepts “on the fly” ; yet it offers people that you are trying to communicate with a good chance to figure out your meaning. In this way, Lojban has a flexible vocabulary which can be expanded indefinitely.
All brivla have the following properties:
always end in a vowel;
always contain a consonant pair in the first five letters, where y and apostrophe are not counted as letters for this purpose (see Section 4.6);
always are stressed on the next-to-the-last (penultimate) syllable; this implies that they have two or more syllables.
The presence of a consonant pair distinguishes brivla from cmavo and their compounds. The final vowel distinguishes brivla from cmevla, which always end in a consonant. Thus da'amei must be a compound cmavo because it lacks a consonant pair; .lojban. must be a cmevla because it lacks a final vowel.
Thus, bisycla has the consonant pair sc in the first five non- y letters even though the sc actually appears in the form of sy.. Similarly, the word ro'inre'o contains nr in the first five letters because the apostrophes are not counted for this purpose.