"Pass The Peas";"Le Freak"; "Get up and Jump";"Shake your Pants""The Crunge"....They all use very similar chords in a Funk setting - what are some Standard Funk Chords and why (from a Music Theory Perspective) have these chords evolved into being embraced as such?
Some of the most popular chords in funk include E9, E7, and E7+9 (also widely known as the so-called "Hendrix Chord", since Jimi used it in "Purple Haze" and other songs), transposed as necessary. Here are their canonical voicings:
E9 and E13 (Often, players will play these without the bass note):
$A.7.$D.6.$G.7.$B.7.$e.7 | $A.7.$D.6.$G.7.$B.7.$e.9
Example song: "Sex Machine" by James Brown (played in Eb rather than E).
Example song: "Who's Gonna Take The Weight" by Kool & the Gang
Example song: "Flashlight" by Parliament
Update: A little love to the Am7 and Am9 chords as used in funk:
$D.5.$G.5.$B.5.$e.5 | $D.5.$G.5.$B.5.$e.7
And the Em11:
As to why these chords became popular funk chords, the most simplistic answer is "Because the R&B musicians who went on to develop funk (James Brown, George Clinton, etc.) used these chords a lot, and for whatever reason, their songs sold lots of records, so the chords became identified with the 'funk' sound and other funk musicians copied them."
A less simplistic but more speculative answer would point out that these are all dominant chords, and that funk, like the blues, doesn't really adhere to the harmonic principles of Western diatonic music. From the diatonic perspective, dominant chords---the E7+9 chord, especially---don't make any sense when used as I and IV chords, as funk does all the time ("Flashlight", for example, is built entirely around a I-IV progression, with seventh chords used for both). The E7+9 is particularly out of place (again, from Western music theory's perspective) due to it's having both a major and a minor third in it.
But again, funk and blues aren't really based on Western music theory principles but instead on African rhythms and harmonies, filtered through Western instruments. In the purest 12-bar blues form from which funk evolved, all the chords are dominant 7th chords, and the scales are based around pentatonic plus blues notes---decidedly not the traditional Western major scale. So it's a bit of a mistake to try to analyze these genres of music from the perspective of Western music theory, since they don't really fit in that context.
etc... etc.. etc.. (google is your friend)
A basic funk chord is Em9 played on the top 4 strings. It is very easy to play(just barre across those strings), is movable, and sounds nice, easy to get the funky sound because you can mute the strings easy(just lift up your finger).
Funk is more about style then specific chords. It is syncopated with lots of ghost notes and "rakes". Some chords make it easier to do so and sound more hip than others but ultimately an chords could be used.
As others have pointed out, a lot of what makes chords sound "funk" is using extended chords over basic triads/7th chords (
G13, etc), and the history of funk is well documented (but can be crudely summed up by "some artists played guitar in a similar way and got very popular, so subsequent artists emulated their styles and a genre emerged"). Something that I don't think is emphasised enough though is voicings and play style.
You can quite easily play a
13 chord on the guitar over all six strings (albeit with a few notes missing due to string number limitations) - however, the role of the guitar in funk music is rarely to play big chords which create a wall of sound. A lot of the time funk guitarists don't stray above playing three notes at a time (usually strings 1-3 or 2-4) as the bass guitar (or keyboard or whatever) will fill out the rest of the harmonic space. While the guitar is often pronounced and loud in funk music, it is not the primary instrument and nor is it the main instrument which outlines what chords are implied. You will often see situations where the guitar is seemingly playing a completely different chord to the one implied by the bass guitar, but this is because they are playing the extensions of the chord rather than the full chord itself (eg a guitarist may be playing F-B-E over a G major chord as it is playing the extensions of a G13 chord... if that makes sense). Playing chords where the root note is not at the bottom of the chord, or even played at all, is tricky to get your head around and takes a lot of practice to get good at.
In terms of play style, a funk guitarist will probably play more dead notes than actual chords in any given song; the guitar in funk music is primarily a rhythm instrument. If you listen to By The Way by RHCP, you will hear in the break/verse parts that the guitar is mostly just playing dead, strummed notes with the occasional
Dm - rather than just playing
DM or staying silent. I know that RHCP isn't a classic 80's funk group, but the influence there is obvious... the guitar should almost compliment the drum groove over playing its own distinct part. You will also hear a lot of very precise single-note lines, but these are also complimentary as rhythmic riffs and often are not intended to be the "hook" of the song.
Other answers cover the actual theory and history of funk guitar better, but I thought that an emphasis on how these chords are played was missing and in order to sound like a funk guitarist, this kind of stuff is extremely important to keep in mind.