The article addresses the treatment of certain fundamental passages from Bolzano’s Wissenschaftslehre and Paradoxien des Unendlichen. In these passages, Bolzano describes some of his key concepts such “Multitude”, “Collections” and “Infinite” in the context of mathematical analysis and Set theory. Therefore, I discuss at length the (almost) unknown Contributions to a Better-Grounded Presentation of Mathematics and the appendix On the Kantian Theory of the Construction of Concepts through Intuitions, texts where Bolzano shows his rejection of Kant.El artículo tiene por objetivo analizar ciertos pasajes fundamentales de la Wissenschaftslehre y de las Paradoxien des Unendlichen de Bernard Bolzano en cuanto al análisis conjuntista se refiere. E...