This doctoral dissertation, entitled The expression of probability, uncertainly and conjecture in Spanish and in Modern Greek, deals with the future tenses of the Indicative in Spanish and in Modern Greek, starting with the reasons that aroused our research interest in this field. In a constantly globalized world, the need for foreign language learning is imperative. In particular, Spanish continuously gains ground in the preferences of Greek students. Greek and Spanish share similarities in terms of phonetics, phonology, syntax and semantics, nevertheless the field of linguistic research between these languages remains relatively virgin. For this study we have chosen to study the field of the verbal paradigm, one of the fields where a high number of errors by Greek learners of Spanish are detected and especially the field of the "future tenses”. Considering that tenses do not only express temporal events but also have the capacity to express extratemporal content and meanings that do not always correspond to the value that is traditionally assigned to them, we try to study the mechanisms through the future tenses express probability, uncertainty and conjecture. The present study aims to adequately characterize and explain linguistic affinities and divergences, through a contrastive analysis perspective, of the future and conditional tenses of the Spanish and Greek indicative. For this, we base our analysis on the theory of temporality as proposed for Spanish by Veiga (2008) and elaborated in several subsequent works (among others Veiga 2012, 2013, 2015a, 2015b, 2020; Leontaridi 2019), adapting it at the same time, to the structure of the Greek verbal paradigm. The analysis of the linguistic facts has revealed that the coincidences in the categories of temporality and temporal dislocation that characterize the two languages makes it possible to explain both ‘straight’ and ‘dislocated’ uses of a verbal form, and at the same time show that as far as the latter are concerned, we are dealing with systematic rather than ‘idiomatic’ uses in both languages. Key words: Mood, indicative, tense, future, conditional, temporality, temporal relations, modal functions, conjecture, possibility, posteriority, temporal dislocation.