Like many things in Lojban, tenses may be logically connected; logical connection is explained in more detail in Chapter 14. Some of the terminology in this section will be clear only if you already understand logical connectives.
The appropriate logical connectives belong to selma'o JA. A logical connective between tenses can always be expanded to one between sentences:
20.1) mi pu je ba klama le zarci
I [past] and [future] go-to the market.
I went and will go to the market.
means the same as:
20.2) mi pu klama le zarci .ije mi ba klama le zarci
I [past] go-to the market. And I [future] go-to the market.
I went to the market, and I will go to the market.
Tense connection and tense negation are combined in:
20.3) mi punai je canai je ba klama le zarci
I [past] [not] and [present] [not] and [future] go-to the market.
I haven’t yet gone to the market, but I will in future.
Example 20.3 is far more specific than
20.4) mi ba klama le zarci
I [future] go-to the market.
which only says that I will go, without claiming anything about my past or present. “ba” does not imply “punai” or “canai”; to compel that interpretation, either a logical connection or a ZAhO is needed.
Tense negation can often be removed in favor of negation in the logical connective itself. The following examples are equivalent in meaning:
20.5) mi mo'izu'anai je mo'iri'u cadzu
I [motion] [left-not] and [motion] [right] walk.
I walk not leftward but rightward.
20.6) mi mo'izu'a naje mo'iri'u cadzu
I [motion] [left] not-and [motion] [right] walk.
I walk not leftward but rightward.
There are no forethought logical connections between tenses allowed by the grammar, to keep tenses simpler. Nor is there any way to override simple left-grouping of the connectives, the Lojban default.
The non-logical connectives of selma'o JOI, BIhI, and GAhO are also permitted between tenses. One application is to specify intervals not by size, but by their end-points (“bi'o” belongs to selma'o BIhI, and connects the end-points of an ordered interval, like English “from ... to”):
20.7) mi puza bi'o bazu vasxu
I [past] [medium] from ... to [future] [long] breathe.
I breathe from a medium time ago till a long time to come.
(It is to be hoped that I have a long life ahead of me.)
One additional use of non-logical connectives within tenses is discussed in Section 21. Other uses will probably be identified in future.