Regarding your questions, for 1, Can you clarify how you define a comprehensible and plausible solution? as worded, this is more a "can your answer pass my not yet clear test?" than an objectively answerable question.

For 2, define similar system. Do you mean a system that tries to have a universal account of morality? Do you mean a system ostensibly based on universalizing maxims? Do you mean something else?

Separately I do have to agree with both answers so far that the maxim you propose seems to be a hypothetical rather than categorical imperative since because you like X is the condition upon which you would buy X -- but liking or not liking X is contingent (unless liking or not liking X is a fact of reason).

Fair enough, it does sound a bit unclear. I mean something that fits what Kant himself says in his texts and that is coherent and doesn't produce other false positives or negatives. I'd also be alright with something that didn't fit Kant's text exactly, if it it fixed the problems and there was good enough reason to support it.

A similar system, I was simply thinking of a deontic system which had a universalization criteria or test, as well, though it could different from Kant's, or, alternatively, a deontic system which would be give an universal account of morality.

Well, I think I phrased my maxim wrong. But it should be read like this : Always buying X (action) whenever I can buy X (condition) because I like X (reason). Liking X would be the reason as to why you chose to adopt that maxim to guide your actions and not another, similar to ''out of self-love'' in Kant's example of suicide ''out of self love''.

Incidentally, this example isn't mine. But it's supposed to be understood as to follow this pattern : If C (condition), then I’ll A (action) for the sake of R (reason). I'm sorry for the confusion.

First off, edit the question rather respond to me in comments regarding changes that clarify your question.

Second, if you are finding the example in the literature, where on earth is the example coming from then? If C (condition), then I’ll A (action) for the sake of R (reason) does not sound categorical at all. Or maybe to word things differently, "I like X" is not at all something Kant would categorize as a categorical reason for action (you or your source may be equivocating on meanings of the word "reason").

Right now the source escapes me, but it's important to remember that you can't just shop for a maxim as a description of your action, you in acting act from a specific maxim that you actually have. Thus, your point about descriptions has much less weight than it seems.

Fair enough, I edited my OP. This specific example (about selling-buying) I took from reading an article by Richard McCarthy published in like 2014-15 I don't really remember, but I also read it elsewhere in different forms (buying but not selling stock, or selling only at X price, but not buying at said price). On the forms of maxims in general (if C, then A for R), multiple recognized authors talk of this, like Kosgaard. Kosgaard explains why this is so and how it could affect the validity of some maxims, but not others. I cited her 1985 paper below. I believe Allen Wood says similar things.

Also, I think I might have explained myself very poorly. When I mean ''because I like X'' as a reason, it is my reason for acting or choosing a certain maxim over another. As Kosgaard explains, the categorical imperative is a test to determine the moral sufficiency of that reason and the maxim adopted as a consequence of it. If it passes, it is morally permissible ; if it fails, it is immoral. The question you ask when you adopt such a maxim is not whether or not it can fulfill the goal or reason that made you adopt it, which would make your line of questioning a hypothetical imperative.

Rather, you ask if the reason and the maxim which was chosen as a consequence of that reason is morally sufficient, valid. This implies the use of the categorical imperative. The reason is anterior to any moral reasoning ; the moral reasoning comes afterwards (categorical imperative) to determine your maxim's moral status.

On the shopping of maxims, I actually agree that if someone in real life were to think of reformulating his maxims to make them into false negatives or positives and ''trick'' the system, he'd be dishonest, and the real maxim upon which he'd act wouldn't be the maxim he tested using the categorical imperative.

However, I think it's also possible to imagine a scenario where someone completely honest could adopt such maxims separately. For instance, one might really like toy trains (reason) (McCarthy's example) and decide to buy toy trains (action), whenever he found one on sale (condition). After a while, he might have accumulated such a collection of toy trains, that he wouldn't want to depart with them since he liked them so much (reason), and decide to never sell toy trains (action) (here the question of conditions is a bit iffy, but it'd be something like under all situations).

Therefore, both of his maxims adopted separately might be moral, since they seem to pass the test. However, in effect, this is the same as if he were to have adopted them together, which would have made his maxim and following it immoral.

On the topic of equivocal meanings of reason, could you elaborate a bit?

I know multiple authors cite Kant's example of suicide (action) out of self-love (reason) as an example of a maxim including the reason as to why it was adopted. But Kant also used other examples, even very specific examples, like knowing you're in financial trouble and making a false promise to payback a loan you know you cannot pay back in order to solve your difficulties (''to solve your difficulties'' being your reason) (I'm obviously paraphrasing, but it's something to that effect).

If you want another example, Kosgaard corrects a maxim which states that we should kill children at night that cry too much to include the reason behind the maxim. She says (in Kant's Formula of Universal Law 1985) : ''We can make the maxim one of killing children that tend to cry at night more than average, in order to get enough sleep.'' And she says that ''in order to get enough sleep'' would be the reason behind the maxim. I'm not a philosophy student or graduate, and I might have gotten the literature wrong, I'm still currently reading on it, but it seems clear, unless I'm wrong.

I haven't published it but I have a draft of a paper where I argue that Korsgaard misunderstands reason pretty badly in Kant, but the equivocation is that Kant means by reason a mental faculty that stands above the understanding rather than a justification (I do x because y -- y is generally a justification/reason rather except when y = because I am rational).

To reword that, when Kant says you act on the basis of reason, he means you act on the conclusions of a maxim that can be universalized as the course of action of all rational creatures -- not that you do A because of some R. That you do A because you are R. On the standard reading A because of some R is not a hypothetical imperative. Korsgaard is a bit clearer on this in the text after Sources of Normativity (= oxfordscholarship.com/view/10.1093/acprof:oso/…) because she was pressed on this point by her interlocutors there and after.

I'm quite lost to your example ( example of suicide (action) out of self-love (reason) as an example of a maxim including the reason as to why it was adopted). There's no place where Kant is okay with suicide in any of his works. The closest you will get is MM in the quodlibetal questions but there the point is that one can will something that includes one's death but not with that as the goal when that action is done to preserve other rational beings (= double effect). Though I guess I do recall, Korsgaard suggesting Kant could be okay with suicide.

Maybe to draw a moral from the story: don't try to read Kant via the Rawlsians. First try to read Kant, then decide if you're a Rawlsian and thus amenable to their re-interpretation.

First, thanks for the answer, clears up some things! On the question of suicide, I wasn't saying Kant thought it was okay, I was citing it as an example as where it seems as though Kant is including a reason within the formulation of his maxim (out of self-love). I agree that Kant thinks suicide is wrong in most scenarios.

On the equivocity of ''reason'', that does seem to be a good explanation for it. Could you redirect me to some passages of Kant which supports this, if possible? And if possible, how would you reformulate the maxim(s) which I have used in my example to fit the correct template? Would the R, be the same in all people of good character, or as I have read, of all people who share the supra-maxim of putting morality (or reason) before their desires? Could you provide an example of what it would be?

On the example I provided, why do you think it would be wrong, if we excluded from it the ''because I like X'', why would it not be a false positive/negative or a contradiction (if you assume the person formulating the maxim is honest and could have been honest formulating it separately)?

Finally, who should I read on Kant? I already read Kant myself (not all his works, but the three main critiques, the groundwork and the prolegomena - not claiming I have a perfect understanding though), since I used to adhere to his moral doctrine, but I encountered some difficulties, which the literature has called often times false positives or negatives, and I couldn't find anyway to solve those questions.

I'm open to any interpretation of Kant, or even dissents from it or from Kant, as long as it leads to a coherent and valid system of morality. I don't think I've settled on any or have the pretension to have the knowledge to be able to, simply from the fact that those I have read cite some of Kant's work which I have not read, or cite it in German, which I do not speak or read.

Would the R, be the same in all people of good character, or as I have read, of all people who share the supra-maxim of putting morality (or reason) before their desires? Could you provide an example of what it would be? Reason (for Kant) is the same for everyone and should lead everyone to the same actions. This can be seen both in GW and in Religion among other texts. This is not a maxim of choice -- instead it's a necessary maxim for rational beings to choose. (Kant makes this point very clear in defining the CI).

Finally, who should I read on Kant? There's quite a few good Kant scholars and quite a few interesting derivative Kantian -- enough so that I'm not going to answer that in a comment.

I'm open to any interpretation of Kant, or even dissents from it or from Kant, as long as it leads to a coherent and valid system of morality. I can't really help you there. There's not that much agreement on what is "valid" and "coherent." You'd have to flesh that out much more clearly -- and again not really answerable in a comment (and possibly not at all on an SE).

I understand that reason, but I meant it in the context of a maxim. So according to how you understand Kant, how would you formulate a maxim correctly? If C, then A?

I understand it's a bit much, but not being a student of philosophy or knowledgeable of works done in that field, is there some place where I might find those interesting Kant scholars? I'm a bit lost at the moment.

By answering in a comment you mean as opposed to a full fleshed answer? So I should just re-make or update my question to include authors on Kant?

Er, I mean ask a separate question in the SE like "who are some of the leading contemporary scholars for understanding what Kant wrote?" / that seems to be separate than asking how to deal with the problems in Kant's formulation of the term maxim.

one could demonstrate to be true and coherence are really tall orders. If one could find that, everyone would follow that view. What's more likely is that there are things you find necessary or expect that would make certain views appear incoherent to you.

Well, alright, I'll ask that if I don't get answers on the false positives/negatives. On that note, do you have a solution or explanation for those? Or a way to avoid them?

I understand those are tall orders, and it's fair enough. But ideally that's what I'm looking for, I just don't want something that just fits my views or that I like better. Ideally, I'd like to have a moral system because it's rational to have it.

Also, thanks a lot for your insights.