We introduce tense LM
_n
-algebras and tense MV-algebras as algebraic
structures for some tense many-valued logics. A representation theorem for
tense LM
_n
-algebras is proved and the polynomial equivalence between tense
LM
_3
-algebras (resp. tense LM
_4
-algebras) and tense MV
_3
-algebras (resp. tense
MV
_4
-algebras) is established. We study the pairs of dually-conjugated
operations on MV-algebras and we use their properties in order to investigate
how the axioms of tense operators are preserved by the Dedekind-MacNeille
completion of an Archimedean MV-algebra. A tense many-valued propositional
calculus is developed and a completeness theorem is proved.