I propose a discussion on my PDF-PowerPoint "A position in contemporary ontology: E.J. Lowe’s interpretation of metaphysics" - I used the PDF-PowerPoint for the lecture held at the National Scientific Conference dedicated to the Day of the National Awakening and the World Day of Philosophy on 3rd November 2023, organised by the Section "Philosophical Sciences" at the Union of Scientists in Bulgaria. In my inquiry, I should like to develop some aspects of E.J. Lowe’s ontological project. The foundations of Lowe’s four-category ontology will be described, and the realistic feature of Lowe’s categories will be underlined. My analysis will present the components of this ontology, represented by substantial particulars, non-substantial particulars, substantial universals, and not-substantial universals. Moreover, I shall discuss Lowe’s use of the distinction between substance and property, on the one hand, and between particular and universal, on the other hand, which lies at the basis of the construction of the ontological square. Thereafter, the notions of objects, kinds, modes, and properties together with the relations, which hold between entities, of instantiation, characterization and exemplification will be analysed. The ontological structure consisting in occurrence and in disposition will be investigated. Particular attention will be dedicated to Lowe’s interpretation of the indispensability of universals both for a correct ontology and for a correct explanation of the scientific phenomena. Furthermore, Lowe’s strategy for the defence of universals and of their existence against all theories which aim to eliminate any presence whatsoever of universals from the ontological field will receive due attention. The application of the ontological square to the theory of scientific explanation will be, afterwards, dealt with. Comparisons between Lowe’s four-category ontology and alternative ontologies such as Armstrong’s concept of ontology based on individuals and on universals, or Campbell’s tropes ontology will likewise make part of my exposition. In particular, Lowe’s interpretation of the laws of nature as such, founded on the concept of the dispositions possessed by the entities will be compared with Armstrong’s interpretation of the laws of nature, which is founded on the relationships of necessitation between universals. Furthermore, I should like to dedicate my attention to Lowe’s meditation on the criteria for being substance. In connection with this subject, I shall analyse Lowe’s interpretation of the indispensability of metaphysics for every interpretation of the entities and of the phenomena regarding entities. I shall first examine Lowe’s criteria of ontological dependency in their connection to the concept of substance. Then, I shall investigate Lowe’s interpretation of substance and of the entities which can be correctly regarded as being substances. Finally, I shall analyse Lowe’s differentiation between substantial change and phase change together with the connection between substantial change and ontological categories. This last subject will be bound to the question of the unavoidability of the metaphysics for a correct interpretation of the different possible sorts of changes, since, for instance, in order that substantial change and phase change can be correctly differentiated from each other, the understanding of the organization of the reality in kinds proves to be indispensable. The main work of Lowe that I will refer to for my exposition will be “The Four-Category Ontology”; nonetheless, I shall, of course, consider concepts exposed by Lowe in his works “Kinds of Being”, “A Survey of Metaphysics”, “More Kinds of Being” and “The Possibility of Metaphysics”. As works of authors maintaining an alternative or, at least, a different ontological theory and an alternative, or, at least, a different theory of scientific explanation in comparison with Lowe’s interpretation, I shall refer, for instance, to Armstrong’s “A Theory of Universals” (volume 1 and 2), to Armstrong’s “What is a Law of Nature”, to Armstrong’s “A World of States of Affairs”, to Campbell’s “Abstract Particulars”, to Ellis’ “Scientific Essentialism” and to Ellis’ “The Metaphysics of Scientific Realism”. These comparisons will aim to show the points of advantage which, in my opinion, Lowe’s ontology possesses both over alternative models of ontology and alternative models for scientific explanations. Furthermore, in order to show the problem of the determination of criteria for being substance in contemporary ontology, I shall compare Lowe’s criteria for an entity’s being substance with the criteria for an entity’s being substance exposed in the works of Hoffman and Rosenkrantz “Substance among other categories” and “Substance: Its Nature and Existence”; my main attention will, however, always be concentrated on Lowe’s analyses. Bibliography D.M. Armstrong, Universals & Scientific Realism, Volume I: Nominalism and Realism, Cambridge University Press, Cambridge, UK, 1978; Volume II: A Theory of Universals, Cambridge University Press, Cambridge, UK, 1978. D.M. Armstrong, Universals: An Opinionated Introduction, Westview Press, 1989. D.M. Armstrong, What is a Law of Nature?, Cambridge University Press, Cambridge, UK, 1983. D.M. Armstrong, A world of states of affairs, Cambridge University Press, Cambridge, UK, 1997. P. Butchvarov, Resemblance and Identity. An Examination of the Problem of Universals, Indiana University Press, Bloomington & London, 1966. K. Campbell, Abstract Particulars, Blackwell, Oxford / Cambridge, MA, 1990. R.M. Chisholm, A Realistic Theory of Categories: An Essay on Ontology, Cambridge University Press, Cambridge, UK, 1996. B. Ellis, Scientific Essentialism, Cambridge University Press, Cambridge, UK, 2001. B. Ellis, The Metaphysics of scientific realism, Acumen Publishing, Durham, 2009. J. Hoffman and G.S. Rosenkrantz, Substance among other categories, Cambridge University Press, Cambridge, UK, 1994. J. Hoffman and G.S. Rosenkrantz, Substance: Its Nature and Existence, Routledge, London, 1997. E.J. Lowe, Kinds of Being: A study of individuation, identity and the logic of sortal terms, Blackwell, London, 1989. E.J. Lowe, The Possibility of Metaphysics: Substance, Identity, and Time, Clarendon Press, Oxford, 1998. E.J. Lowe, A Survey of Metaphysics, Oxford University Press, Oxford, 2002. E.J. Lowe, The Four-Category Ontology: A Metaphysical Foundation for Natural Science, Clarendon Press, Oxford, 2006. E.J. Lowe, More Kinds of Being: A Further Study of Individuation, Identity, and the Logic of Sortal Terms, John Wiley & Sons, Malden, MA, 2009. D. Wiggins, Sameness and Substance, Blackwell, Oxford 1980. D. Wiggins, Sameness and Substance Renewed, Cambridge University Press, Cambridge, UK, 2001. N. Wolterstorff, On Universals: An Essay in Ontology, The University of Chicago Press, Chicago and London, 1970.