In the Critique of Pure Reason, Kant states that ideas give us the rule for organizing experience and ideals serve as archetypes or standards against which one can measure copies. Further, he states that ideas and ideals can be practical. Understanding how precisely these concepts should function presents a challenging and understudied philosophical puzzle. I offer a reconstruction of how ideas and ideals might be practical in order to uphold, to my mind, a conceptually worthy distinction. A practical idea, I (...) argue, is best understood as a reference to the categorical imperative (and its various formulations), which guides conduct directly as a rule. A practical ideal, by contrast, I think is a substrate that serves two functions: one that (a) helps us gauge moral deficiencies and another that (b) reveals the potential for moral improvement. In response to well-grounded sceptical concerns, I argue that ideals are indirectly practical in that they ground the possibility to recognise moral states of affairs and be moral in the first place. (shrink)

In this paper, we re-examine a series of gedanken welcher Weg (WW) experiments introduced by Scully, Englert and Walther that contain the essential ideas underlying the quantum eraser. For this purpose we use the Bohm model which gives a sharp picture of the behaviour of the atoms involved in these experiments. This model supports the thesis that interference disappears in such WW experiments, even though the centre of mass wave function remains coherent throughout the experiment. It also shows exactly (...) what it means to say ‘that the interference can be restored by manipulating the WW detectors long after the atoms have passed’. It does not support Wheeler’s notion that ‘the past is undefined and undefinable without the observation (in the present)’. (shrink)