Guys I'm in the midst of studying jazz. And I'm so confused whether jazz is the same as blues, especially the rhythm parts If blues is using shuffle, then jazz is using swing? Then why sometimes blues is also using jazz rhythm?
Blues and Jazz are overlapping genres, so it won't always be possible to characterise a song as 'jazz, but not blues' or 'blues, but not jazz'.
It would be possible to write a very big book about the characteristics of blues, and probably an even bigger one about the characteristics of jazz, but very briefly, blues tends to...
- Make use of the blues scale
- Have simple arrangements centred around guitar, piano, and voice
- use fairly simple chord progressions, most typically the 12-bar blues chord progression
- lyrically, emphasise themes of hardship and struggle
These are huge generalisations - What is it about the blues chord progression that makes the blues feel? goes into a bit more detail.
jazz, on the other hand -
- tends to use more complex chord progressions, with an emphasis on substitution and variation
- uses a wide range of scales
- uses a lot more brass, and bigger ensembles, than blues songs
- in some forms, tends to use more dance rhythms
- has a stronger latin influence
Again, these are generalisations, and in the early days of jazz and blues, many of the same influences were feeding into both blues and jazz, and typical blues forms were (and continue to be) used in jazz.
An example of a song that (I feel) is both blues and jazz is Strange Fruit:
The scale used in the vocal delivery and lyrical theme are very bluesy, but the chord progression and trumpet part speak to the Latin influence on the jazz idiom.
As topo morto said, it won't always be possible to decide whether a given song is Jazz or Blues. However, there is one thing that's striking about blues and sets it apart from most genres, including in particular Jazz: in Blues, the accompaniment prefers to use the same chord-flavour on every functional degree, irrespective of whether this seems to fit in the key's scale. The historical reason is that many influential Blues guitarist, very notably Robert Johnson, used slide guitar for accompaniment a lot, which can't very well change harmonies in any other way but moving the entire chord up or down the neck.
The most characteristic case is that all chords are seventh chords (“dominant” seventh chords, but the term is absurd here because they don't act as dominants). Classically, with the 12-bar progression Ⅰ7 - Ⅳ7 - Ⅰ7 - Ⅴ7 - Ⅳ7 - Ⅰ7 - Ⅴ7. It won't always be so clear-cut – more modern blues does also switch chord genders occasionally, and it certainly doesn't always use seventh chords, but it definitely doesn't put multiple chords in a row with each chosen in a way to conform to any particular scale.
In particular in contrast to Jazz, you don't normally find any major seventh chords in Blues.
If it shuffles rather than swings, and is built on the '12-bar blues', it's very likely Blues. If it's played by guitar (maybe piano) and vocal, and the lyrics are about the misfortunes of daily life, the genre is pretty well confirmed.
Fairly safe to say that if it ISN'T a 12-bar, and ISN'T shuffle, it isn't classic blues.
But music is all about cross-influences. Don't sweat over borderline cases. Interesting to see 'Strange Fruit' mentioned. I wouldn't force that one into any genre. 'Political Art music, with blues and jazz infulences' perhaps.
The main difference between blues and jazz is the way pitch is used. It is this which I'll discuss briefly in this answer. Simply put, jazz focusses much more on the harmonic aspect, whereas blues on the microtonal melodic aspect.
Blues sits in the tradition of microtonal field hollers, microtonal African American music which is melodic in nature, and doesn't rely on harmony as a device at all, in terms of pitch, the expressiveness comes from melody, and microtonal inflection. Blues has a sprinkling of harmony, but this harmony is always fundamentally subservient to the melody (I could go into a lot more detail on this but I'd be here for a while. There are a couple of different ways harmony can manifest itself in blues but that's another question)
If any one thing is a cornerstone of "blues", then it's "blue notes". That is to say, singing or playing notes that sit outside of the western scale. They are not fixed pitches, but spaces which are explored, creating a very deep expressiveness. These most significantly are the intervals of blues thirds and tritones.
As a typifying example, Hendrix playing an instrumental born under a bad sign is perfect. The melody of the guitar is a masterclass in blue notes https://open.spotify.com/track/1HbOlAS9kF9d5j7WNQbin9 (not on youtube any more but please listen to Hendrix - Born under a bad sign!!!!) And and earlier example:
Jazz is more harmonic, I'll come back and add more detail later. For later jazz, it's easy peasy lemon squeezy to distinguish it from blues, so I won't bother: to go into much detail. Suffice to say there are complex "jazzy" harmonies, and a harmonic framework based fundamentally on discreet pitches (the ones on the piano). Even when playing "a blues", it will be constructed of these 12 notes, and almost certainly full of substitutions and harmonic colour.
For earlier jazz there is more of a crossover. While early jazz does include some blue notes, it's within a framework of ensemble playing illustrating a harmonic progression: bent and blue notes are gravy rather than the fundamental structure of the song itself. For an example of this, listen to potato head blues (one of the best recordings ever made?): the song is definitively jazz, but if you listen to the clarinet part in the solo, he plays around with blues thirds as a cheeky sounding and definitely "bluesy" embellishment. Nevertheless, the fundamental context is "jazzy", they're illustrating chord progressions with their playing, painting a picture of a harmonic environment with their melody lines. This isn't the function of melody in blues at all.
For an example of more modern jazz not easy to mistake with blues, here (also an excuse to share some fantastic music):
As an aside, the "blues scale" as an idea is a much later invention, pinned on to blues by non blues musicians, and largely misses the point altogether. It can at a stretch be useful to improvise along to the blues if you really want, no one with good ears and a passing familiarity with the blues could tell you with a straight face that the blues is "based on the blues scale" any more than Bach is "based on the pentatonic scale".