Why can parts of masterworks in philosophy be skipped?

Question

TL/DR: This question presumes reading of a philosophical work for fun and self-learning.

How did philosophers err or underperform, and so enable or justify some skipping? Did they repeat themselves redundantly; digress; write poorly compared to other parts?

---

Optional Reading (The following only quotes advice on what to skip):

For example, Reddit's Flaired user 'ben_profane' advises on 2014/6/17:

'Heidegger and phenomenology are important and all, but a super deep understanding of them aren't really necessary'.

Reddit's Flaired user 'TychoCelchuuu' on 2015/12/5 advised:

I would not skip Locke's Second Treatise on Government. I am not sure reading Kant's Critique of Practical Reason is a good use of time. Thoreau could be cut.

Reddit's user 'paschep' on 2015/12/5 advised:

I think you should only read the three major parts of The Critique of Practical Reason, the rest doesn't really matter. Also I would highly recommend the critique of pure reason over all the other Kant works.

I think you should add Heidegger's Being and Time and the analytic philosophers (eg. Kripke, Quine).

I think you really should read the most important parts of these books, there are many parts that can be skipped.

Reddit's Flaired user 'irontide' on 2016/1/4 advised:

No, it isn't important to read a philosophy book back-to-back
[StackExchange User 'Timere' : The author meant 'front-to-back'].
There are very many books that are classics in the field but which almost nobody reads back-to-back as a rule but instead deals with extracts: two examples are Hobbes's Leviathan and Hume's Treatise. And reading them in excerpts is more charitable than not doing so, because these works are of uneven quality. People only care about the middle third of the Leviathan and especially don't buy Hobbes's claim that the physical theory in the first third entails the political theory in the second (and basically just ignore the last third, on the church), and Hume's Treatise is a big book of him flinging shit at a wall and seeing what sticks (not all of it does: the arguments concerning mathematics in there are pretty much an embarrassment, and his political philosophy in there is famously unconvincing). But the bits people do read is stuff so vital and important we teach it to undergrads, despite Hobbes's paper-thing arguments against his opponents and Hume's overweening love for his own opinions.

Answer 1

I think the general notion I would call upon here is that "Whoever does something first, very seldom does it best, and almost never does it most efficiently." But they will be the reference, as the source, for all time.

Information is ecological. A major work of philosophy places ideas in the public domain that are then evolved and assimilated, and ideas related to or consequent upon those become broadly distributed and easy to understand. But when those very same root ideas are first presented, they need to be laid out in gory detail and expressed from multiple perspectives, or they will not be communicated.

Once the notion is refined by passing through many hands and has become accessible by standard examples, reading the original presentations that considers them new is often painful and annoying. At the same time, those ideas are compromised by their assimilation. So you also cannot necessarily expect any secondary source to capture everything that might be relevant to you. The author will unwittingly put a given 'spin' on things that may be foreign to the original.

Unlike philosophy, one very seldom reads mathematics in the original, which makes it an even better example of why doing so in philosophy is often not efficient.

Turing's conjecture of the existence of the universal machine, for instance, is painful and bizarre, given that we all use computers daily, and the people most likely to read it have written in assembly languages and understand mechanical logic quite well. We have no trouble accepting his premise, and the actual construction is hard going for no gain. We want to get on with the actual ideas, as if this wasn't one.

Reading Galois' notes from the eve of his death is almost impossible, he is so intelligent that he makes tremendous bounds, and you cannot follow him, in certain places, but so little of basic combinatorics existed that in other places he torturously belabors points we all know. You cannot choose a speed at which to read.

Some primary-source philosophy is equally pointlessly demanding.

(In my experience, the closer to math it is, the more likely this is to be true. I have found it easy to read Plato in the original, but not Kant or Hegel, despite that Greek itself has always been much, much more demanding for me than German was at the time I was trying to do such things. I think this is not just the form, but the distance of the ideas from delicate processes and intricate balances.)

Answer 2

I can think of at least three relevant ways that "famous philosophers" write that wind up being skippable in a general overview of philosophy. (I suggest the phrase "famous philosophers", because a hidden premise in the question of asking why we skip parts of Kant is that it's somehow less problematic that we aren't read reams of Wolff, Baumgarten, and others).

First, there's the seminal idea factor. We don't read Aristotle to learn dentistry even though he comments (mistakenly and inexplicably) on the number of teeth women and men have. Thus, parts that are erroneous and largely accepted to be merely incidental to their philosophies can be skipped. We're looking for the ideas that made them famous and the arguments that make them interesting to us. Thus, we're interested in Descartes' rationalism, Hume's skepticism, Kant's transcendental apparatus, etc. etc. (Of course, there are minority positions on how to read the history of philosophy, but this is the main one).

Second, there's the writing quality factor. Usually, famous philosophers are famous for reasons beyond just having seminal ideas (or rather ideas that look seminal to us). Thus, we're also looking (especially in an overview) for the clearest version of idea rather than just the first. So, for instance, Aristotle seems to have an unmoved mover and uncaused cause argument in Metaphysics and Physics, but Aquinas offers a much cleaner and easier to follow version of the same. This isn't a singular principle as sometimes the there's not many versions to choose from that make a point (who other than Heidegger makes the same claim about the "problem of Being"?)

Finally, there's tediousness. This kind of ties into the second point but I don't think it's identical. Augustine's unedited City of God contains lengthy and repetitive refutations of Roman gods. Few today care about the issue there. Similarly, Leviathan or Locke or Hegel talk a lot about kings and their roles in political philosophy, but these arguments just look tedious unless that's your particular specialization.

A fourth principle though not a factor is that a "masterworks" approach to philosophy must by necessity accept that not everything is of equal interest to all. Picking four philosophers who periodically show up here, Colin is going to be much more interested in philosophy of math questions, shane medieval philosophy, Dr. J contemporary continental, and myself modern German philosophy. To each of us, these are going to be more interesting to you average reader, but we'd all probably accept that people should understand say key thoughts by Plato, Descartes, Hume, and Kant.