At the center, logically and often physically, of every Lojban bridi is one or more words which constitute the selbri. A bridi expresses a relationship between things: the selbri specifies which relationship is referred to. The difference between:
1.1) do mamta mi
You are-a-mother-of me.
You are my mother.
and
1.2) do patfu mi
You are-a-father-of me.
You are my father.
lies in the different selbri.
The simplest kind of selbri is a single Lojban content word: a brivla. There are three different varieties of brivla: those which are built into the language (the gismu), those which are derived from combinations of the gismu (the lujvo), and those which are taken (usually in a modified form) from other languages (the fu'ivla). In addition, there are a few cmavo that can act like brivla; these are mentioned in Section 9, and discussed in full in Chapter 7.
For the purposes of this chapter, however, all brivla are alike. For example,
1.3) ta bloti
That is-a-boat.
That is a boat.
1.4) ta brablo
That is-a-large-boat.
That is a ship.
1.5) ta blotrskunri
That is-a-(boat)-schooner.
That is a schooner.
illustrate the three types of brivla (gismu, lujvo, and fu'ivla respectively), but in each case the selbri is composed of a single word whose meaning can be learned independent of its origins.
The remainder of this chapter will mostly use gismu as example brivla, because they are short. However, it is important to keep in mind that wherever a gismu appears, it could be replaced by any other kind of brivla.