In hac dissertatione primitiae laborum philosophicorum Leibnizii, scil. Disputatio metaphysica de Principio Individui, examinantur et quidem itam ut Leibnizii sententia cum doctina Suarezii in Disputationibus Metaphysicis proposita comparetur. Lebnizii et Doctoris Eximii de hoc principio opiniones in multis concordant: Uterque enim auctor quaestionem de individuatione pure ontologice pertractat, uterque idem principium individuationis materialibus et immaterialibus tribuit, uterque nominalismo quodammodo favet Hoc ex conclusionibus, quas defendunt, elucet, et modo, quo sententias adversarias (Scotisticam praesertim) impugnant, confirmatur. Affinitas quaedam non solum inter dictorum auctorum doctrinam de principio individuationis conspicitur, sed et alibi, e. g. in doctrina de distinctione inter essentiam et existentiam, de untiate transcendentali eiusque habitudine ad ens, de principiis substantialirum materialium apparet.

The article examines the first fruit of Leibniz´s philosophical endeavour, which is his baccalaureate thesis Disputatio metaphysica de Principio Individui, on the background of the comparison with Suárez´s conception of individual unity in his Disputationes Metaphysicae. Despite Suárez´s more differentiated attitude to the issue of individuation in general, the author is convinced that one can find strong parallels between both authors, namely the following: purely ontological treatment of the problem of the principle of individuation; search for a single principle which is common both to material and nonmmaterial substances; nominalist tendency, which is apparent not only in the positive statements of the two authors, but also in their criticisms of rival solutions in general, and the Scotist conception in particular. The similarities are not limited only to the principle of individuation or to the problem of individual unity in general but they also extend to the problem of the distinction between essence and existence, the conception of transcendental unity and its relation to ens, or to the problem of reification of hylemorphic components of material substances.