His main work, On the Content and Object of Presentations (1894), established the need for the distinction between the content and the object of a presentation within Brentanian theories of the intentionality of mental acts.
His Habilitationschrift (1894) concerned the concepts of the content and the object of presentations; it clarified and sharpened this important distinction.
Twardowski's main publication in the Vienna period is, next to his doctoral dissertation Idea and Perception (1891), his Habilitationsschrift, On the Content and Object of Presentations (1894), Twardowski's most influential work.
When one does so, one should keep in mind however that these concepts do not properly pick out objects of presentation.
By contrast, the objects of presentations are intuitively present, i.e., they stay "in front of" the subject as in perception, imagination, presentification, etc., and therefore can stretch in time.
Novel object, side of presentation, and context were counterbalanced within and across days where relevant.
The psychological content of a presentation is something immanent, but it is usually not an immanent object in the sense of both being the object of the presentation and also existing inside the presentation.
This special case is the case in which the content of some presentation plays the role of the object of another presentation.
The object of a presentation, says Twardowski using Zimmermann's terminology, is that which is presented in a presentation; the content is that through which the object is presented.
