Up until now, I've just been practicing triads on all major/minor keys. If I wanted to play jazz, do I just add sevenths (ie dominant7, major7, minor7) to chords in my chord progressions or is it a lot more involved than that? (I'm guessing it is.)
Jazz is an unbelievably expansive genre with over 100 years of musical tradition; a big part of this tradition is an ever-increasing list of sub-genres that fall under the larger umbrella term of "jazz."
Your "(I'm guessing it is)" is encouraging; it suggests you realize it's maybe a little silly to think you can mimic such a broad tradition by "just randomly add[ing] sevenths." It's a bit like asking if we can mimic Classical music by "just randomly adding cellos."
But more than that, you've unintentionally simplified jazz to just one musical feature: harmony.
The jazz genre includes particularities of rhythm, of meter, of instrumentation and voicing, of articulation, of interpretation, of phrasing, you name it. And included in that list, yes, is harmony.
Suggesting that you can play jazz just by adding sevenths suggests that the only thing that makes jazz jazz is harmony, which is clearly not the case. Playing jazz requires an awareness (and eventually mastery) of everything that makes jazz jazz, not just this one feature.
In other words, playing jazz takes quite a bit more than adding sevenths. All great things take time and patience, and jazz is no exception.
If you're asking about first steps in jazz piano, most people would suggest, as you've intuited, learning your ii7–V7–I7 pattern in all major and minor keys; doing so will teach you quick resolutions of minor sevenths, dominant sevenths, and half-diminished sevenths built on all twelve chromatic pitches.
Ninths are good too! Even thirteenths.
Yes, there's more to jazz than extended chords, though you'll certainly need more than triads to play it, so start learning m7, maj7, 9, b9 etc. chords so they're ready for when you work out what jazz IS.
And that's a big question. Start with a New Orleans Blues, travel to Miles Davis and beyond... But whatever style you choose to explore first, yes you'll need some 7th chords.
If you're really into rock/pop and just want a quick, easy jazz flavour, slip in a 'b5 substitution'. In place of Dm7, G7, C impress your friends with Dm7, Db7, Cmaj7. But again, yes you'll need a vocabulary of 7th chords to even start this.
But don't try to enter the world of jazz through the 'theory'. Get some jazz sheets and learn the chords you need to play them.
If you are trying to move towards learning jazz, you should learn your 7th chords (esp. dominant, major, and minor). After you get the hang of these, you can learn less common 7ths as well as extended chords out to 9/11/13. If you are not too familiar with jazz, the most important thing you can do is to listen to a lot of good music in this genre.
To keep things simple, I would suggest starting with blues. It is technically its own genre of music, but the form is simpler and the harmony tends to be less complicated.
If I wanted to play jazz do I just add sevenths (ie dominant7, major7, minor7) to chords in my chord progressions or is it alot more involved than that? (I'm guessing it is).
This very abbreviated list should help you answer this question:
- The Jazz Language: A Theory Text for Jazz Composition and Improvisation
- Jazz Theory Resources: Volume 1
- Jazzology: The Encyclopedia of Jazz Theory for All Musicians
- Fundamental Changes in Jazz Guitar: An In Depth Study of Major ii V I Bebop Soloing: Master Jazz Guitar Soloing
- The Jazz Theory Book
@Richard's answer explains why these books were written and are popular, as well as numerous others.
Another very easy way to answer your question: Look through a book like this, and see how well you do *by just adding sevenths (ie dominant7, major7, minor7) to the chords instead of the suggested chords, which often include far more than just 7th chords. * :
When I was playing rhythm guitar in a swing band there were many times when I would only play root, third and fifth of a chord as the horns were (many times) covering the 'weird' notes. So, in chording for jazz you don't always need the 7th and beyond.
As Richard stated above - there is much more to playing jazz (or other genres) than just the chord patterns chosen. There is much to explore. That's what is so wonderful about learning and playing music - there is always something new to learn. I've had classical and jazz guitar lessons. Played bass (with no training) in a rock band. I now play acoustic and electric guitar at church doing praise & worship stuff and also play mandolin and guitar in a bluegrass band. I'm continually learning new stuff as that's what keeps me interested (I do the same in my day job as a software geek).
There are different types of sevenths. Let us take the key of C Major as there are no sharps or flats.
C to B is a major 7th. C to Bb is a minor 7th and C to Bbb or A is a diminished 7th. Now as C to A is also a 6th (Count C to A,include the C) a little education on scales and intervals (the difference in two different sounds) will help you to appreciate how it works and increase your enjoyment.