The following cmavo is discussed in this section:

The normal Lojban sentence is just a bridi, parallel to the normal English sentence which has a subject and a predicate:

In Chinese, the normal sentence form is different: a topic is stated, and a comment about it is made. (Japanese also has the concept of a topic, but indicates it by attaching a suffix; other languages also distinguish topics in various ways.) The topic says what the sentence is about:

The colon in the first two versions of Example 19.3 separate the topic (“this news”) from the comment (“I know already”).

Lojban uses the cmavo zo'u (of selma'o ZOhU) to separate topic (a sumti) from comment (a bridi):

Example 19.4 is the literal Lojban translation of Example 19.3. Of course, the topic-comment structure can be changed to a straightforward bridi structure:

Example 19.5 means the same as Example 19.4, and it is simpler. However, often the position of the topic in the place structure of the selbri within the comment is vague:

Is the fish eating or being eaten? The sentence doesn't say. The Chinese equivalent of Example 19.6 is:

which is vague in exactly the same way.

Grammatically, it is possible to have more than one sumti before zo'u. This is not normally useful in topic-comment sentences, but is necessary in the other use of zo'u: to separate a quantifying section from a bridi containing quantified variables. This usage belongs to a discussion of quantifier logic in Lojban (see Section 16.2), but an example would be:

The string of sumti before zo'u (called the “prenex”: see Section 16.2) may contain both a topic and bound variables:

To specify a topic which affects more than one sentence, wrap the sentences in tu'e…tu'u brackets and place the topic and the zo'u directly in front. This is the exception to the rule that a topic attaches directly to a sentence:

Note: In Lojban, you do not “want money”; you “want to have money” or something of the sort, as the x2 place of djica demands an event. As a result, the straightforward rendering of Example 19.9 without a topic is not:

where ri means loi jdini and is interpreted as “the mere existence of money”, but rather:

namely, the possession of money. But topic-comment sentences like Example 19.10 are inherently vague, and this difference between ponse (which expects a physical object in x2) and djica is ignored. See Example 19.45 for another topic/comment sentence.

The subject of an English sentence is often the topic as well, but in Lojban the sumti in the x1 place is not necessarily the topic, especially if it is the normal (unconverted) x1 for the selbri. Thus Lojban sentences don't necessarily have a “subject” in the English sense.