I think what comes down to measuring the difficulty of a text is the method used and the way that it is written. When I say this, many would be thinking about the split between analytical and continental philosophy and their methods. This split is usually an academic one. I mostly read continental works and therefore I will be somewhat bias here. I don’t necessary hate on analytical thoughts, but it seems inevitable that if you put a continental and an analytical thinker in the same room, they will eventually end up in a debate (like John Searle and Jacques Derrida).
Most of my philosophical journeys are made on my own (though I have taken philosophy courses on ethics, film theory, history, etc). And over the year, I feel like I have made a significant progress in understanding Jacques Derrida (I read Derrida without secondary commentary sources). My interest in philosophy mostly lies within media (photography, film, etc), aesthetics, phenomenology and language. This is probably because of my photography background.
The Analytical tradition
Although I am no expert at it, analytical philosophy in general are written in crisp clear arguments. After all, clear logical arguments written in ordinary language is what they are consistently proud of. But their entire scope of the argument might be huge (say, linguistics), which would make their writings difficult to understand. Analytical methods often strives on logic, clarity and mathematics. They consider their own work as parallel to natural sciences. In short, analytical philosophers writes philosophy with little to no regard about its relevance to history most of the time. They are ideas that can stand on its own through pure logic and reasoning.
I can’t really give insight on how to read these because I am not a fan of how they write.
Continental tradition came from mainland Europe. My experience with continental thinkers is that they tend to include and consider the history of philosophy along with their own ideas (think about Hegel or Kant). Thus, there are no simple way of addressing philosophy because everything is connected. For continentals, it is naive to write about philosophy and not consider historical discourses. Hence, continental philosopher’s works will tend to be written in response to other philosophers works (ie. Derrida responding to Heidegger, Saussure, Husserl, Hegel, Plato, Aristotle etc). Therefore, to understand one philosopher, you must also understand the previous, where such philosopher also writes according to another, etc. This would ultimately turn continental philosophy into a highly technical text, loading it with a very complex prose which will often frustrate the reader, causing misreadings or a complete disregard of their ideas. Not to mention that the history of philosophy is over two thousand years old.
Furthermore, continental thinkers rejects natural science as the most accurate way of interpreting our everyday phenomena. There are several reasons for this, but one being the idea how natural sciences are based on a certain phenomenon. A phenomenon which is pre-logical, and pre-theoretical (experiences that comes before a theory or language is created). It is only after one interprets such phenomenological experience (via an articulation through a language, or an episteme of sorts) where it becomes a science of something.
Reading Continental Philosophy
The best way to learn continental works is to keep reading them. The more you read it, the easier it gets. Sometimes, even if you don’t understand something, you should just keep going because they might explain it in a different way 200 pages later. Keep in mind that you don’t always have to read entire books of major works (there are exceptions). You have to learn when you can just encyclopedia some of the philosophers that so and so are talking about, or find secondary sources. Yes, by reading a secondary source, you will miss out many important detailed information, but as long as the secondary source is reliable, then you should be “okay” for now.
There are a lot of reputable secondary sources that are quite readable. But if that is still too hard, you can try writers like Alain de Botton, he seems pretty easy (maybe a bit too easy). Reading original works in original language is preferred. The next best thing are translations from well known translators (for example, scholars who translates Derrida are esteemed Derridean thinkers; ie. Geoffrey Bennington, Gayatri Chakravorty Spivak, or Leonard Lawlor). Again, secondary sources are acceptable in certain situations (ie. Christopher Norris is also a world leading Derridean intellectual who writes commentary on Derrida, but not a translator of Derrida’s works). Most of the time, you also want to make sure that you are reading books from reputable university publishers like Cambridge, Chicago, Oxford, Stanford, Columbia, Johns Hopkins, etc (though this is not always true).
Many continental works are written in a non-linear format. Each chapter somewhat functions simultaneously to its former and latter chapters / sections. So it is up to you on how you can synthesize these concepts at once (Lacanian psychoanalysis is a good example). This takes practice, and it is also arguably one of the most important skills in reading such books. It gets easier over time.
Continental philosophy are the type of philosophy where you have to reread in a few years down the road. Especially after you have read other continental books. As one of my teachers like to say, these books leaves crumbs that you pick up and piece back together from the crumbs of other books. Not to mention that it is often such crumbs which will get you to read other continental books or lead you into sculpting a new idea. It will help you learn about the different discourses that so and so might be talking about.
In general, I would say that continental philosophy requires an acquired taste (knowledge) from past experience to enjoy.
Continental writing takes many different forms, some appears with a more poetic prose (Nietzsche, Kierkegaard), while others appears as different forms of art (Pollock, Godard, Beckett, who were all known for being a part of the existential movement), mathematics (Badiou), or other highly technical apparatuses. I personally think that continental thoughts are closer to real life than analytical. There are of course, other philosophers before the continental and analytical split (or pre-Kantian) that were amazing. For example, Jean Jacques Rousseau (the father of romanticism), and Renes Descartes.
Not all continental works are as hard as the Critique of Pure Reason, Phenomenology of the Spirit, Of Grammatology, Ecrits or Being and Time. For example, some of the writings from Roland Barthes are easier than to understand than others. Even when his ideas are actually quite complex when you analyze it. In his narcissistic book, A Lover’s Discourse, Barthes consistently speaks about the “Other”. This concept of the Other is made famous by several prominent continental scholars such as Lacan, Hegel, Levinas and Derrida. In general, Barthes had a huge influence on post-structuralist thinkers like Jean Baudrillard whose later works are not written academically, but in a rather “romantically pessimistic” tone (not surprising, since Baudrillard was Barthes’ student). Baudrillard is famed for practicing a certain type of writing called pataphysics (one should not be surprised that pataphysics is recognized as pseudoscience).
If phenomenological experiences are pre-logical and pre-theoretical, then some of these thinkers will be obscure. This is because what comes before our interpretation of such experience will always remain uncertain. This obscurity is where this famous “gap” lies – between phenomenon and our interpretation (or in a Derridean sense, our articulation) of it. Another words, we can never fully interpret the phenomenon that we experience in front of us through the production of meaning and languages. Most importantly, for thinkers like Baudrillard (and even more so for Derrida), we tend to interpret / produce only the things we desire to see out of a particular phenomenon.
From personal experience, if you start reading late 20th century continental (post-structural) works, you will begin to recognize that often times, the reason why you don’t understand something is because you are still thinking within the structure of language (to be fair, that is all we can really do…but not really, say for example: love, spirit, and grace). Understanding post-structural continental works don’t just require good reading comprehension and vocabulary (which I am terrible at), but also a large capacity for imagination. You must think with an open mind and beyond the structure.
Existentialism and Phenomenology
I don’t have much experience with reading existentialism. But from reading Derrida and Baudrillard who were both heavily influenced by Nietzsche, I can tell you that existentialism is quite a different breed of continental philosophy. 20th century philosophy and “postmodern philosophy” has been incredibly influenced by existentialism. It is like what Derrida has said about Nietzsche, he “has written that writing”. Where as Martin Heidegger is often known for combining existentialism and phenomenology called existential phenomenology. The same goes for Jean-Paul Sartre who famously and very influentially writes in between philosophy and literature. Sartre was also known for declining the Nobel Prize in 1964. Other incredible existentialists includes, Soren Kierkegaard, Simone De Beauvoir, Albert Camus and Maurice Merleau-Ponty. Furthermore, existentialism can also be seen as a cultural movement. As already mentioned, renown novelists like Samuel Beckett, artist Jackson Pollock, or French New Wave film director Jean-Luc Godard are often associated with it.
Phenomenology on the other hand, while being quite slippery, was an incredibly influential discipline. It is as the study of phenomena from a conscious first person point of view, such as the way you are reading this text, and how you hear yourself speak in your head (auto-affection); or how we experience our everyday phenomenon of reality, signs, time, our body, touching, feeling, seeing, hearing, etc. It was invented by Edmund Husserl who furthered the split between analytical and continental philosophies. His book Logical Investigations influenced many 20th century continental works including Heidegger, Derrida, Sartre, and Merleau-Ponty. 20th century was the century of phenomenology.
Reading and Learning with Passion
Given its technical sophistication, is there even such a thing as casually reading continental philosophy? I’m not sure. I would say that continental philosophy (and even analytical, but again I have no experience in that regards) requires a huge amount of determination. You really need to love it in order to understand it. And when you teach it to someone else, your passion will really show. Most importantly, don’t give up. You will always run into people that think you are insane or accusing you of making things up because you are thinking the unthinkable.