The following cmavo are discussed in this section:

This section has two purposes. On the one hand, it explains the grammatical construct called “modal sentence connection”. On the other, it exemplifies some of the more useful BAI cmavo: the causals. (There are other BAI cmavo which have causal implications: ja'e means “with result”, and so seja'e means “with cause of unspecified nature”; likewise, gau means “with agent” and tezu'e means “with purpose”. These other modal cmavo will not be further discussed here, as my purpose is to explain modal sentence connection rather than Lojbanic views of causation.)

There are four causal gismu in Lojban, distinguishing different versions of the relationships lumped in English as “causal”:

Each of these gismu has a related modal: ri'a, ki'u, mu'i, and ni'i respectively. Using these gismu and these modals, we can create various causal sentences with different implications:

In Example 9.35 through Example 9.38, the same English word “because” is used to translate all four modals, but the types of cause being expressed are quite different. Let us now focus on Example 9.35, and explore some variations on it.

As written, Example 9.35 claims that the plant grows, but only refers to the event of watering it in an abstraction bridi (abstractions are explained in Chapter 11) without actually making a claim. If I express Example 9.35, I have said that the plant in fact grows, but I have not said that you actually water it, merely that there is a causal relationship between watering and growing. This is semantically asymmetrical. Suppose I wanted to claim that the plant was being watered, and only mention its growth as ancillary information? Then we could reverse the main bridi and the abstraction bridi, saying:

with the ri'a changed to seri'a. In addition, there are also symmetrical forms:

does not claim either event, but asserts only the causal relationship between them. So in Example 9.40, I am not saying that the plant grows nor that you have in fact watered it. The second colloquial translation shows a form of “if-then” in English quite distinct from the logical connective “if-then” explained in Chapter 14.

Suppose we wish to claim both events as well as their causal relationship? We can use one of two methods:

The compound cmavo .iri'abo and .iseri'abo serve to connect two bridi, as the initial i indicates. The final bo is necessary to prevent the modal from “taking over” the following sumti. If the bo were omitted from Example 9.41 we would have:

Because ri'a do is a modal sumti in Example 9.43, there is no longer an explicit sumti in the x1 place of djacu dunda, and the translation must be changed.

The effect of sentences like Example 9.41 and Example 9.42 is that the modal, ri'a in this example, no longer modifies an explicit sumti. Instead, the sumti is implicit, the event given by a full bridi. Furthermore, there is a second implication: that the first bridi fills the x2 place of the gismu rinka; it specifies an event which is the effect. I am therefore claiming three things: that the plant grows, that you have watered it, and that there is a cause-and-effect relationship between the two.

In principle, any modal tag can appear in a sentence connective of the type exemplified by Example 9.41 and Example 9.42. However, it makes little sense to use any modals which do not expect events or other abstractions to fill the places of the corresponding gismu. The sentence connective .ibaubo is perfectly grammatical, but it is hard to imagine any two sentences which could be connected by an “in-language” modal. This is because a sentence describes an event, and an event can be a cause or an effect, but not a language.