 Both the notion of an object ‘immanent’ in a mental act, as well as, in all generality, the term ‘object’ in Brentano's Thesis, have an ambiguous character. Are the objects of mental acts fully inside us or not? To correctly judge that the aether does not exist means, in Brentanian terms, rejecting the aether which is given to one's consciousness by a presentation. But if the aether is an object immanent in me, fully inside my consciousness, what does it mean, then, that I reject it? Is it some mental entity inside my consciousness that I reject? But how could that possibly be correct? In this case I most certainly have something in my head, and that something exists. So it cannot be correct that I reject it—for, if that is the aether I reject, the judgment that the aether does not exist cannot be true. The aether should be a physical space-filling substance, outside my consciousness: that is what I am rejecting. But if that is what I reject, it seems something must be there for me to be able to affirm that it is not there. This is very puzzling. It was fundamentally due to difficulties of this kind that Brentano's theory of judgment was subjected, from 1889 onwards, to continuous objections by philosophers such as Sigwart and Windelband. Brentano engaged in the debate in his defense, as did his pupils Marty and Hillebrand. It is in this context that Twardowski's Habilitationsschrift was conceived. Twardowski saw that notions such as ‘the object of a presentation’ and ‘immanent object’ were ambiguous because in Brentano's writings the object of a presentation was identified with that of content of a presentation (Twardowski 1926, 10). In Content and Object, Twardowski set out to clarify exactly the relationship between the two, with far-reaching implications for Brentano's original position.