According to a recent post by Eric Schliesser on the NewAPPS Blog, “Scientific philosophy has six characteristics”, which by and large repeat the six points made in his earlier article in HoPoS about “Newton’s Challenge”:

1. Empirical ‘success’ trumps other (rational/methodological) claims. Given that scientific philosophers sometimes retreat to the idea that philosophy is an a priori discipline, the ’empirical’ (in 1) is often re-packaged as, say, inference to the best explanation in light of a variety of enduring ‘scientific virtues’ (i.e., simplicity, scope, predictive power, fruitfulness, exactness, etc.)
2. (a) Physics is the foundational science and/but it (b) has no need for ultimate foundations. While 2(a) may seem obvious (see, e.g., Ladymann & Ross) due to its universal scope, its foundational nature was contested well into the nineteenth century. One could imagine, say, the science of information taking over as the foundational science in the future.
3. Within scientific philosophy reason limits itself in various ways: in doing so (a) it avoid the fallacy of systematicity because it does not try to say everything about everything; (b) it embraces the intellectual division of labor (from 3(b)); it avoids the fallacy of (metaphysical) foundationalism because it has no need to try to to secure its practice in un-shakeable, first principles (see 2(b)). So, it is no surprise that Russell rejected the principle of sufficient reason or Bradley’s regress argument.
4. Scientific philosophy is a self-directed, autonomous practice; once one has mastered certain rigorous tools, one moves from one given experiment/solution (etc.) to the next problem. Given the emphasis on rigor, it is no surprise that:
5. Scientific philosophy is often opposed to a licentious or unintelligible alternative(s) associated with past failures, sometimes even moral. It, thus, embraces commitments to transparency (and clarity).
6. Scientific philosophy offers submission to the facts and is disciplined by way of a careful, painful, modest and most importantly open-ended progressive method. This entails that any scientific philosopher will enter a pre-existing, moving research trajectory and can expect to die before any destination is ever reached.

How would Brentano’s ideal of Philosophy as Science fit into such an account?

1. “There is no doubt anymore that also in philosophical matters no other teacher can be found than experience, and that it is not a matter of revealing the whole of a more complete Weltanschauung as a product of genius, but that a philosopher, like any other researcher, can only make progress in his field conquering it step by step.” (Brentano, Über die Gründe der Entmutigung auf philosophischem Gebiete, p. 85)
2. “the true method of philosophy is none other than that of the natural sciences” (Brentano’s 4th habilitation thesis) Physics is the model for the empirical scientific method, but it is not the foundational science and does not supply the fundamental ontology of reality. Brentano sharply distinguished physical from psychical phenomena and the epistemic strength of our external and internal perceptions of them: “Internal perception is actually the only kind of perception in the proper sense, while strictly speaking so-called external perception isn’t perception.” (Brentano Psychologie vom empirischen Standpunkte, 119) Which leads to: “Every natural law is an hypothesis” (Husserl’s 1st habilitation thesis)
3. a) “We are taking the first steps towards the renewal of philosophy as science”, not by conjuring up “proud systems” out of thin air, but by humbly “cultivating fallow scientific ground” (Brentano “Über Schelling’s Philosophie”, 131). b) It is well known that each of Brentano’s students concentrated on specific field under his guidance: Stumpf, the philosophy of sound and music; Marty, the philosophy of language; Meinong, the history of philosophy, esp. British empiricism; Husserl, the philosophy of mathematics; etc.
4. “Our teachers and leaders will be those that … have performed truly scientific work, sober, detailed research based on the facts, in the field of philosophy” (Brentano, “Über Schelling’s Philosophie”, 131) Stumpf explains how this would work concretely in his lectures on psychology: through analysis and comparison of individual perceptions we induce a general rule as hypothesis, we then deduce and predict particular cases, and empirically verify their actual occurrence. The more rigorous the method, the more exact its results.
5. Brentano never wastes an occasion to trash the German Idealists and the speculative method: “Their works are to be condemned as utterly, unreservedly, from the beginning to the end, completely worthless”, “The inner worth of our investigations is infinitely superior precisely to these speculations” (Brentano, “Über Schelling’s Philosophie”, 127, 130) In Brentano’s account of the repeating cycles of four phases of philosophy, Plotinus and Hegel represent the most extreme cases of decadence as opposed to the peaks of scientific and purely theoretical philosophy of Aristotle in antiquity, Aquinas in the middle ages, and then Bacon, Descartes, Locke, Leibniz in the modern era (guessing the peak of Brentano’s contemporary philosophy is left as an exercise to the reader …).
6. I think the quotes I supplied for the other points leave no doubt about these characteristics. Brentano and his students, however, do stress that natural science, since it relies on external perception, always remains hypothetical and hence open-ended. Scientific philosophy, on its turn, would also require a completely matured scientific psychology, which at the time wasn’t yet fully developed and still a work in progress.

Moreover, based on these points, it certainly seems like the School of Brentano also has the main traits which Schliesser contends elsewhere to be typical of analytic philosophy: “Analytic philosophy was self-consciously founded a) against the great man approach to philosophy [let’s call that “the magisterial approach”], and accepting, by contrast, b) the division of intellectual labor, such that c) philosophy is a collective enterprise.” However, Brentano is not trying to answer “Newton’s Challenge”, simply by answering philosophical questions through natural science. To the contrary, while using the same method of the natural sciences Brentano also aims at establishing a proper domain for the Geisteswissenschaften. In other words, he makes room for philosophy as an unnatural science.