Secondary qualities are properties that a thing appears topossess for certain observers of this thing. On reflection, however, secondaryqualities turn out to be ways in which certain observers are affected by thething in question. Colors are an example. Colors are not genuine propertiesinherent in things but rather ways in which human beings with normal eyesightare affected by certain things they encounter. Secondary qualities are thus to be explainedby reference to both: the object with its “primary” qualities and the perceptual apparatus of a specificobserver of this object. The doctrine of secondary qualities brings with it thethought of the object as it is apart from whatever qualities it merely appearsto possess for certain observers. You can call this the thing it itself, thething considered apart from its merely apparent, observer-dependent properties.So the two expressions you query are not at all synonymous but rathercorrelative: “thing in itself” refers to an object as it is apart...

Immanuel Kant used this word in the titles of his most important books, and Kant's use has greatly influenced the sense this word has in later philosophy. By a critique Kant means a critical examination, which will sometimes criticize or undermine a view or method but sometimes also justify and vindicate it.

The journal Ethics and International Affairs had a symposium on this question very recently, see www.ethicsandinternationalaffairs.org/2012/summer-2012-issue-26-2/ -- focused mostly of the topic of world poverty as addressed by the new organization Academics Stand Against Poverty (www.academicsstand.org). <Fair disclosure, I have been involved with both ASAP and the E&IA symposium.>

Kant's transcendental idealism explains the fact that experience presents us objects in a certain spatio-temporal order about which we can have some a priori knowledge by reference to a human capacity, our sensibility, through which alone we can become aware of objects. According to this explanation, space and time are then features only of objects as they appear to us. Confronted with this explanation, we are prone to ask what these objects are like apart from our sensibility, apart from how they appear to us (as spatio-temporal). Within Kant's own account, the concept of a thing in itself answers to this reflection: a thing in itself is any ordinary object (including event) considered apart from the spatio-temporal features it has by virtue of being an object for us (i.e. for beings with our human sensibility). Things in themselves are then the familiar objects of our experience, but considered in abstraction from their spatio-temporal features. And their existence is then no more problematic (if we...

Kant's contradiction in the will test suggests what you say it suggests only on the assumption that, as a rational agent, one necessarily wills one's own existence. Most human beings are happy to be alive, but it does not follow from this that any human (let alone any rational) being must will its own existence. Indeed, some philosophers have argued that, by giving birth to them, their parents violated their rights. So I think the best way to reject the Kantian argument you are suspicious about is to reject its premise that a rational being necessarily wills its own existence. Something Kant did think rational beings necessarily will is the continued existence of rational life. Using this premise instead, we might get a moral rule against abortion when the survival of the human race hangs in the balance. Suppose rational beings found themselves in a world where, if they all took themselves to be permitted to act on the maxim to have an abortion whenever doing so promises a more pleasant life,...

You suggest that Kant's criterion of wrong conduct turns on this question: "If everyone acted the way I am proposing to act, would this have undesirable consequences?" I think Kant's actual question differs in two respects. Kant is not asking whether the agent would like some fictional world (find it desirable), but whether the agent can will it and her own proposed conduct in it. And the world Kant envisioned is not one in which all act the way the agent is proposing to act, but one in which all are permitted (and take themselves to be permitted) so to act. So Kant's question is: "Can I will the action I am considering along with its universal permission?" The basic idea here is that I should not permit myself an action that I cannot permit all others at the same time. Let's see how this plays out in Kant's promising example. The agent considers extricating himself from financial difficulty by making a false (lying) promise. He then asks himself whether, in a world in which all took themselves to...

Plato calls in his Republic for women to participate as equals in the activities of citizenship, saying that surely many women are more excellent than some men and that less excellent women should be disqualified from various roles (along with less excellent males) on account of their lesser excellence rather than on account of their gender.

I used exactly this example in an essay published over 20 years ago as one of the arguments in support of a more subtle interpretation that had been first proposed by Tim Scanlon. On this reading, it is the permission one is claiming for oneself that is to be universalized. So instead of asking whether one can will that all people act on one's maxim of remaining childless, one is to ask instead whether one can will that all people be permitted to remain childless. In the world as it is, we can certainly will this universal permission (because enough others would decide to conceive even without a duty to do so), and therefore each of us is permitted to act on the maxim in question.

A case very similar to the one you imagine is found in Kant's writing. The case is so widespread in academic life that we can be pretty sure that Kant was speaking from experience. An author comes up to you and asks: "How do you like my publication?". Well, you actually don't think much of it at all. So what to do? Kant considers that there may be some (perhaps humorous) way of avoiding a straight answer; but it must be found very quickly, because the author has his eyes firmly fixed on you and will be distraught at the slightest hesitation. So is it alright to mislead this poor author -- perhaps with adjectives such as "interesting", "amazing", "unexpected", "special", "solid", "painstaking", which, in his hunger for confirmation, he will understand as praise for the quality of his work? Is it alright to stretch words beyond ordinary vagueness, saying that it's a "good" book, or at least a "decent" one -- or that you "got a lot out of it" or "enjoyed reading it"? Kant doesn't answer his question....

Kant believed that you should only permit yourself to do what you could will all others to be permitted to do as well. So you are to ask yourself: what if the maxim on which I am about to act were available to all others as well? Here is an example. Hijackers are holding 200 passengers hostage in a plane. They are threatening to kill passengers one by one unless their demands are met. Being the designated police negotiator, you might be able to win time by telling them, falsely, that the government is making arrangements toward meeting some of their demands. Here Kant would say: suppose your proposed maxim -- lie to hijackers to postpone the execution of hostages -- were universally available. Then everyone would understand that such lies are permissible. And then hijackers could not be influenced by such lies -- they, too, would know that in a situation like the present you are permitted to lie. So the lie you are about to permit to yourself can work only because this permission isn't universal...