5.6. Logical connection within tanru

The following cmavo are discussed in this section:



tanru logical and



tanru logical or



mixed mass and



tanru forethought logical and



forethought connection separator

Consider the English phrase big red dog. How shall this be rendered as a Lojban tanru? The naive attempt:

Example 5.39. 


will not do, as it means a dog whose redness is big, in whatever way redness might be described as big. Nor is

Example 5.40. 


much better. After all, the straightforward understanding of the English phrase is that the dog is big as compared with other dogs, not merely as compared with other red dogs. In fact, the bigness and redness are independent properties of the dog, and only obscure rules of English adjective ordering prevent us from saying red big dog.

The Lojban approach to this problem is to introduce the cmavo je, which is one of the many equivalents of English and. A big red dog is one that is both big and red, and we can say:

Example 5.41. 


Of course,

Example 5.42. 


is equally satisfactory and means the same thing. As these examples indicate, joining two brivla with je makes them a unit for tanru purposes. However, explicit grouping with bo or keke'e associates brivla more closely than je does:

Example 5.43. 


big yellowish-red dog

With no grouping indicators, we get:

Example 5.44. 


biggish- and yellowish-red dog

which again raises the question of Example 5.39: what does biggish-red mean?

Unlike bo and keke'e, je is useful as well as merely legal within simple tanru. It may be used to partly resolve the ambiguity of simple tanru:

Example 5.45. 


definitely refers to something which is both blue and is a house, and not to any of the other possible interpretations of simple blanu zdani. Furthermore, blanu zdani refers to something which is blue in the way that houses are blue; blanu je zdani has no such implication – the blueness of a blanu je zdani is independent of its houseness.

With the addition of je, many more versions of pretty little girls' school are made possible: see Section 5.1 for a complete list.

A subtle point in the semantics of tanru like Example 5.41 needs special elucidation. There are at least two possible interpretations of:

Example 5.46. 


It can be understood as:

Example 5.47. 

That is a girls' school and a beautiful school.

or as:

Example 5.48. 

That is a school for things which are both girls and beautiful.

The interpretation specified by Example 5.47 treats the tanru as a sort of abbreviation for:

Example 5.49. 


whereas the interpretation specified by Example 5.48 does not. This is a kind of semantic ambiguity for which Lojban does not compel a firm resolution. The way in which the school is said to be of type beautiful and girl may entail that it is separately a beautiful school and a girls' school; but the alternative interpretation, that the members of the school are beautiful and girls, is also possible. Still another interpretation is:

Example 5.50. 

That is a school for beautiful things and also for girls.

so while the logical connectives help to resolve the meaning of tanru, they by no means compel a single meaning in and of themselves.

In general, logical connectives within tanru cannot undergo the formal manipulations that are possible with the related logical connectives that exist outside tanru; see Section 5.1 for further details.

The logical connective je is only one of the fourteen logical connectives that Lojban provides. Here are a few examples of some of the others:

Example 5.51. 


the runner(s) is/are winner(s) or loser(s).

Example 5.52. 


skin which is blue only if it is cold

Example 5.53. 


speech which is good if (and only if) it is short

Example 5.54. 


speech which is important, whether or not it is pleasing

In Example 5.51, ja is grammatically equivalent to je but means or (more precisely, and/or). Likewise, naja means only if in Example 5.52, jo means if and only if in Example 5.53, and ju means whether or not in Example 5.54.

Now consider the following example:

Example 5.55. 


which illustrates a new grammatical feature: the use of both ja and bo between tanru components. The two cmavo combine to form a compound whose meaning is that of ja but which groups more closely; jabo is to ja as plain bo is to no cmavo at all. However, both ja and jabo group less closely than bo does:

Example 5.56. 


rich and (blue or greenish-blue)

An alternative form of Example 5.55 is:

Example 5.57. 


In addition to the logical connectives, there are also a variety of non-logical connectives, grammatically equivalent to the logical ones. The only one with a well-understood meaning in tanru contexts is joi, which is the kind of and that denotes a mixture:

Example 5.58. 


The ball described is neither solely red nor solely blue, but probably striped or in some other way exhibiting a combination of the two colors. Example 5.58 is distinct from:

Example 5.59. 


This is a bluish-red ball

which would be a ball whose color is some sort of purple tending toward red, since xunre is the more important of the two components. On the other hand,

Example 5.60. 


is probably self-contradictory, seeming to claim that the ball is independently both blue and red at the same time, although some sensible interpretation may exist.

Finally, just as English and has the variant form both ... and, so je between tanru components has the variant form gu'egi, where gu'e is placed before the components and gi between them:

Example 5.61. 


is equivalent in meaning to Example 5.41. For each logical connective related to je, there is a corresponding connective related to gu'egi in a systematic way.

The portion of a gu'egi construction before the gi is a full selbri, and may use any of the selbri resources including je logical connections. After the gi, logical connections are taken to be wider in scope than the gu'egi, which has in effect the same scope as bo:

Example 5.62. 


something which is either big, red, and a dog, or else a cat

leaves mlatu outside the gu'egi construction. The scope of the gi arm extends only to a single brivla or to two or more brivla connected with bo or keke'e.