“An aspect of Bolzano’s influence on Husserl which is well known is the Husserlian definition of analyticity (Simons, 1992, Ch. 15; Benoist, 1997, Ch. 2). In the Third Logical Investigation, 12, Husserl gives a definition by substitutivity: an analytic proposition is a proposition that keeps its truth-value by substitution of its extra-logical constituents. That definition seems evidently Bolzanian (Bolzano, 1837, 148), and not Kantian.
However, concerning that point, there are also differences. Bolzano’s definition of analyticity is not only a logical one (Proust, 1986). According to Bolzano, there is logical analyticity, but also a more general kind of analyticity (defined by the possibility of substituting a determinate representation of the proposition by any other one, without changing the truth value of the proposition). Bolzano is aware of the difficulty of defining the logical constituents of a proposition as opposed to the other constituents (Simons, 1992, Ch. 2). In that sense, he is very far from the contrast between “formal” and “material” constituents that Husserl defends. Husserl was aware of this because he says that Bolzano completely missed the very idea of a “formal ontology”.
A remaining point may not be as well known: the Bolzanian idea of “synthetic a priori” may also have had a great influence on Husserl’s thought. Bolzano had the idea of synthetic a priori (“internal”) relations between concepts, especially (in his early work: cf. Laz, 1993) concepts related to perception. According to him, there was an a priori of color, as well as of spatial extension, etc. Such ideas (of a “conceptual a priori”, but one concerning intuition) may have played a decisive role in the invention of a phenomenological a priori (Benoist, 1999).
There are, in fact, numerous similarities between Bolzano’s and Husserl’s thoughts, and one may say that, along with Brentano, Bolzano was the author who had the greatest influence on Husserl. We are not, however, to forget the fundamental differences which also separate their ways of thinking. Bolzano was above all a realist. He did not care for constitution problems, and Husserl was right when he wrote in Ideas 94 that Bolzano had no idea of what phenomenology actually was. Certainly, the first stage of Husserl’s thought, which can be called a “realist” one, was much closer to Bolzano’s thought than what came afterward. However, Husserl, who inherited a way of thinking in terms of “acts” from his mentor Brentano, was at that time already of the opinion that consciousness may determine the real, and give an intentional sense to it. The very idea of intentionality is, however, very far removed from Bolzano’s thought, which holds to an absolute realism. Such a position can also explain the fact that Bolzano had no idea of the Husserlian concept of “formal object”, which is bound up in the concept of categorial operations on the object. Consequently, Husserl remarks, not without reason, that Bolzano was much more of an empiricist than he himself was (Husserl, 1913, 9). In Bolzano’s work, a form of semantical realism (and, in another sense, of idealism) is to be found, but no sense of ontological (Platonic) idealities, because Bolzano had no way of constituting them.
The Bolzano-Husserl relation therefore provides an interesting example of a very close relationship, both historical and conceptual, between two ways of thinking founded on very different, even quite opposite presuppositions. Such a paradoxical synthesis may actually constitute the originality of phenomenology, in its unification of both branches (the psychological and the semantical) of the Austrian philosophical tradition.” p. 99
From: Jocelyn Benoist, Husserl and Bolzano, in: Anna-Teresa Tymieniecka (ed.), Phenomenology World-Wide. Foundations – Expanding Dynamics – Life-Engagements. A Guide for Research and Study, Dordrecht: Kluwer, 2002, pp. 98-100