Hegel, Petronijević held that our immediate experience is the source of basic logical and metaphysical axioms – what he called "empirio-rationalist" epistemology.

His father changed Branislav's last name to reduce pressure at school, as the Jeremić family were prominent supporters of the exiled Karađorđević dynasty.

After three semesters in Vienna he enrolled at the University of Leipzig, where he studied philosophy under Johannes Volkelt, Wilhelm Ostwald, and Ernst Mach.

After Rome, Petronijević spent several months in Paris, where he taught two courses at the Sorbonne, on universal evolution and on the value of life.

There, Petronijević worked on an English translation of Theoria Philosophiæ Naturalis (A Theory of Natural Philosophy) by Roger Joseph Boscovich, together with Čedomilj Mijatović and Nikolaj Velimirović.

[8] Parts of it were severely criticized by Vladimir Varićak in 1925 for various factual errors, among other things for asserting Boscovich's exclusively Serbian ethnicity, and listing his birth date inaccurately.

[9] While in London, Petronijević met with Bertrand Russell, who wrote: A man who impressed me, not so much by his ability as by his resolute absorption in philosophy even under the most arduous circumstances, was the only Yugoslav philosopher of our time, whose name was Branislav Petroniević.

I admired his capacity for intellectual detachment from the accidents of his corporeal existence, in which I felt that few ancient Stoics could have rivalled him.

During the Interbellum, Petronijević was an active participant in European philosophy, and considered himself a worthy philosopher who transcended his "parochial" limitations.

Although original, his system grew out of the nineteenth-century empirical metaphysics of Hermann Lotze, Eduard von Hartmann and Petronijević's teacher, Johannes Volkelt.

The motto of Petronijević's principal work Prinzipien der Metaphysik (Principles of Metaphysics, 1904), reads: "Exact mathematical notions are a key to the solution of the world's enigma".

Petronijević argued that being consists of simple, discrete qualitative points which are mutually related in various ways to form a unity.

His metaphysical system was thus conceived as a synthesis of Baruch Spinoza's monism and Gottfried Leibniz's monadological pluralism into what he called "monopluralism".

[1] He claimed that the basic task of metaphysics was to explain the structure of the "world of multitude, diversity, and change" as the "pre-evidence" of the directly given empirical and transcendental reality.

Petronijević's view was essentially idealistic, since he held that absolutely unconscious atoms are impossible and that the immortal soul is a conscious monad.

[6] He devoted a number of studies to aesthetics, particularly in the work of Petar II Petrović Njegoš and Leo Tolstoy.

[2] Gavin de Beer, however, disputed this difference, claiming it could be entirely accounted for by deformation of the specimens during preservation, a conclusion generally accepted by later paleontologists.

Wellnhofer (1993) and Tischlinger & Unwin (2004) identified the triangular structure as indeed part of the sternum, albeit minimally ossified (mostly cartilagenous).

This supported the idea that the Berlin Archaeopteryx was not a full-grown individual at the time of its death, and instead represents an immature animal.

[4][5] After the extensive examination of five newly discovered early bird specimens all of his taxonomic interpretations were abandoned, and only his discoveries of the Archaeopteryx skeleton parts remained.

In 1923, Petronijević added a new species, M. ancestrale to the genus Moeritherium, excluding a skull and a mandible from those attributed to M. lyonsi on the basis of some cranial characters observed on the palatine and occipital.

In his revision of the genus, Heinz Tobien [de] considered the skull differences mentioned by Petronijević as intraspecific and sex-related variations and synonymised M. gracile, M. lyonsi and M. ancestrale, keeping only one species for the Qasr el Sagha Formation under the name M.