Examining what seems at first to be purely aspecto-temporal morphemes in Wolof (Niger-Congo, Atlantic group, Senegal), such as Present Perfect and Ongoing Present conjugations, or perfective and imperfective suffixes, this paper first brings to light the recurring polysemy of these and their modal values in particular. A thorough examination of their uses in discourse shows that the variation in meaning is quite similar in the different aspecto-temporal morphemes and can be expressed by the following rule: aspecto-temporal specifications yield a temporal expression with dynamic verbs (which is well known) and turn into modal specifications with stative verbs as in the following examples: (1) Present perfect with an action verb lekk naa (ba noppi) eat PFT1sg (until stop) I have eaten (untill it is finished) (2) Present perfect with a stative verb At the end of a discussion where the interlocutors disagree : tàng na ! be-cold PFT3sg (but I tell you) it is hot ! gloss : it is certain, there is no more discussion, there is nothing to be added (3) Perfective suffix () with a stative verb Picc bii moo mel ni ndobin bird this SUBJ.FOC ( =PERF) resemble like calao This bird looks (definitely) like a calao (4) Imperfective suffix with a stative verb Picc bii mooy mel ni ndobin bird this SUBJ.FOC+IMPERF resemble like calao This bird tends to look like a calao More precisely, with the stative verbs, the various aspecto-temporal morphemes in Wolof convey an attitude on the part of the speaker with regard to the certainty (perfective) vs uncertainty (imperfective) or to the completeness (perfective) vs uncompleteness (imperfective) of the process (it is really / not really P), which we may characterize respectively as epistemic and appreciative modality. Moreover, these epistemic values are also associated with regular argumentative effects (the discussion is over / I disagree / I agree / I am relieved / you should do something…) corresponding to what De Smet and Verstraete (2006) call « interpersonal subjectivity ». Thus, through discourse chaining, the same aspecto-temporal morphemes are also used to express various types of engagement on the part of the speaker. It is then argued that in the different uses of these aspecto-temporal morphemes, the same semantic structure is applied to different Aktionsarten producing various semantic effects, that is temporal vs. modal values. These various modal values (ranging from epistemicity to engagement and argumentation) are analysed here as by-products implied by the verb inflection’s aspectual meaning, Eventually, the emergence of these modal senses for aspectual morphemes is described through regular conditioning mechanisms involving Aktionsarten and clause chaining in discourse: the different argumentative effects of the Perfect can be described in terms of various positions of the interlocutors in relation to the process. Therefore the functioning of these Wolof aspectual morphemes shows a regular mechanism of subjectification that may grammaticalize (cf Bybee et al.1994: 74, Traugott 1995) but is also attested in synchrony (Abangma 1985, DeLancey 1997, De Wit et. al. 2013, Robert 1994, Thomas 1978, Wright 1994) and has been probably overlooked in other languages. References Abangma, Sanson Ngebo. 1985. The interrelation between aspect and mood in Denya. Journal of West African Languages XV/2: 110-123. Bybee, Joan, Revere Perkins and William Pagliuca, 1994. The evolution of grammar. Tense, aspect, and modality in the languages of the world. Chicago: The University of Chicago Press. DeLancey, Scott. 1997. Mirativity: The grammatical marking of unexpected information. Linguistic Typology 1: 33-52. De Smet, Hendrik and Jean-Christophe Verstraete. 2006. Coming to terms with subjectivity. Cognitive Linguistics 17-3, 365-392. Astrid, De Wit, Adeline Patard and Frank Brisard. 2013. A contrastive analysis of the present progressive in French and English. Studies in Language, Vol. 37:4, 846–879. Robert, Stéphane, 1994. Sur le rôle du sujet parlant dans la construction du sens : liens entre temps, aspect et modalité. In Marina Yaguello (ed.), Subjecthood and Subjectivity. Paris: Ophrys, 209-230. Thomas,,Elaine. 1978. A Grammatical Description of the Engenni Language. Summer Institute of Linguistics Publications in Linguistics, 60. Dallas: Summer Institute of Linguistics. Traugott, Elisabeth Closs. 1995/ Subjectification in grammaticalisation. In Dieter Stein and Susan Wright (eds), Subjectivity and Subjectification. Linguistic Perspectives. Cambridge: Cambridge University Press, 31-54. Wright Susan. 1994. The mystery of the modal progressive. In Dieter Katovsky (ed.), Studies in Early Modern English. Berlin: Mouton de Gruyter, 467-485.