I am self-learned amateur guitar player and I play for quite long time (around 10 years) and not playing jazz/blues bad but I feel not progressing for a very long time.
The reason is that I have no idea about theory of music like intervals, chord progressions etc.
My question is : How to enter to jazz theory ? Because there are lots of sources that are not accessible for me. Where can I start learning jazz theory by myself ?
As everyone here has already said, the fundamentals are fundamentals. Whether you choose jazz, pop, or hip hop, if you really want to be a better musician and understand music as a language, you must know the fundamentals.
"What are the fundamentals?" Well, the Theory 1 class of Hunter music school defines the fundamentals as the following in their syllabus (see the full syllabus below for a more "classical" approach, i.e, counterpoint):
"Review of music fundamentals, including notation; treble and bass clefs; pitches and their registers; durations and rests; simple and compound intervals; major and minor scales; introduction to modal scales; simple and compound meters; triads; and seventh chords."
So basically, you should know all of those in order for you to "branch off" and focus on jazz. Truthfully, you will also probably need to know some of the basic harmonic progressions as well in order to fully understand tonality (Dominant->Tonic, most core example). Once you know these things, you will be able to effectively learn "jazz theory", which is based off of all this.
With that said, I imagine that most if not all "jazz theory" books out there will include all of the above and teach it to you before moving on to the jazz specific stuff.
Basic classical theory is fairly easy to get into and uses almost the same exact building block that jazz theory uses. Most jazz theory classes someone would take require a basic music theory class as a prerequisite.
There are many sources to get you started in classical theory including MusicTheory.net's lessons which if you can learn and understand them you could dive into more intensive theory books that are geared towards jazz theory.
To understand the theories that are used in jazz, it helps a LOT to first understand the basics, which are contained in what is known as classical theory. In order to appreciate altered chords and scales, it's easier when the original ones are known - the alterations start to make sense then! So start with basics, then branch out once they are known.
In short, I would recommend increased exposure, learning to play specific songs by ear, and having a reference book.
There are always a few different ways to go about learning a new style. One of the more important things is to listen to that style as much as possible. This will ingrain the feel of the style. You can learn a lot of theory from books but that will only get you so far. I have a whole lot of Classical theory (went to school for it) but my writing sounds nothing like it because I have not focused on it and don't listen overly frequently. With that theory I could certainly write closer to that idiom but it takes a lot more thought to be able to. Real point being that the more you listen to it, the more it becomes a part of your style.
The best way to further that sort of learning is to transcribe as much as you can. By learning to play what the greats did, it really sinks into your hands. It's also a much more involved way of listening. It takes you from hearing and feeling, to knowing what notes and rhythms are typically used within the idiom that actually create that feel.
That being said, Jazz theory, while rooted in the same concepts as Classical, is fairly unique. There are a lot of the rules of Classical music that are (somewhat by necessity) completely abandoned, voice leading for example. So having a reference to the theory can be very helpful. There are many books on Jazz theory but the one I am most familiar with and is used in the academic community is Mark Levine's 'Jazz Theory Book'. I learned a great deal from it, personally. A book can be very helpful to provide some insight to things like Extensions and Alterations, which you don't see a whole lot of outside Jazz, though they certainly do exist.
To best learn any style of music, you should try to fully immerse yourself. Allow it to take over your musical world for a while. You can still take some breaks to listen to or play other music but try to keep that to a minimum for a while. I'd say that after a few weeks to a month of full immersion that it would be a good idea to kind of step away from it for a few days, then fully immerse again. That will allow your brain a break and to get back in touch with other styles that you have enjoyed. Then when you return to the Jazz studies you may find increased desire and a new outlook/perspective on the music itself and how to best replicate it. Basically no matter what you are doing, it is always best to give yourself some breaks because it will actually improve your learning ability.
Lastly, even though it sounds like it may not be an option for you, I would very much recommend getting a teacher. A good teacher can recognize what you are doing poorly and what steps to take next for the best approach to learning.
I would probably just be the contrarian here but I do not think there really is such a thing as 'Jazz Theory' as much as there is 'Baroque Theory' or 'Romantic Theory'
A proper understanding of the core principles of music theory and history opens the door up to any style you may want to pursue.
how many lives do you have at your disposal? In case you have only one and you are no more a student (students have or should have a lot of time, that's the point), my suggestion is to start from a Real Book. You'll start playing the pieces with very simple chords on your left hand and single notes on the right side: at the beginning they will sound quite similar to popular songs...not exactly jazzy. But quite soon you will fall in love with those "odd" symbols that go far beyond major and minor. What you need as a baseline: how to stack up note to build major, minor and diminished chords according to classical theory (the simplest!), knowledge of the intervals. A "blues" pentatonic scale to start playing (or jocking!) with notes will help you to get more fun from the beginning both in minor and major chords as soon as you'll start improvising. This recipe worked great with me: if you are curious and interested you'll find out dozens of things and quite soon you will become a jazz enthusiast. Last but not least: listen, listen, listen. As soon as you become familiar with harmony, try to write down the pieces that you like more. One of the best practice, in my opinion, is applying this exercise to very slow and well-known ballads as they are played by famous [jazz] artists: you'll find out how many chords they add (!!) and how the piece still sounds familiar despite of this! Oh, it's great. My best wishes
p.s.: few months ago I bought "Jazz Piano" by Mark Levine. It's really useful in case you have a lot of time to spend regularly on piano (at least one hour per day...just a dream for me). Intervals and chords are at the very beginning....
