Partial Capo Basics
Most people think of the partial capo as an alternative or a substitute to altered tunings. While it is true that they behave in similar ways, and since there are partial capo "equivalents" to a few common tunings, it's a reasonable way to look at the partial capo. However, capos and tunings are not at all the same, and they present different sets of possibilities. It can be frustrating if you are used to using tunings, since you can get only a few of the same sounds with a partial capo. Partial capos can easily be used together with altered tunings, and a number of very fruitful combinations are already in use by some players. Tunings and capos are sort of "mirror images" of each other, and each have their own advantages and disadvantages. They are used for the same reasons, and they give simiar but not identical results. (This may be part of why partial capos are not more widespread. People expect them to be the same as tunings, and don't realize that they present the same kinds of results, but not identical. You can't really play the same music qwith both ideas.) The majority of the deepest and most powerful partial capo ideas involve combining one or more partial capos with altered tunings. Only one of the ideas in Harvey Reid's "Top 10" favorite partial capo ideas uses a single capo in standard tuning.
Before you can grasp how the partial capo works, you need to examine the tuning vs. the capo version of Drop D tuning, since it generates the "Aha!" realization about how partial capos work and how they differ from tunings.
The best way to understand the difference between non-standard tunings and partial capoing is to look at the common Drop D tuning, and compare it with its partial-capo equivalent, which I call Drop E. If you are new to partial capoing, and have a Third Hand, or a Shubb c8b, Kyser "Dropped D" , or other open-jaw style capo that can be used to clamp a Drop E, you may want to read this page with guitar in hand. (If you are using a Kyser Droped D capo, be aware that they call it the "Drop D" capo, which we think is a confusing name since you play in E not D when you use it.)
First Take A Look at Drop D Tuning...
In Drop D tuning the low E string is tuned down one whole step to D. It gives almost any fingering of a D family chord a big tonic bass note. The three bass strings on the guitar are then D, A, and D, two 1's and a strong 5 bass for any D chord. You can play any D or D minor or D7 on the three treble strings anywhere on the fretboard and use all three bass strings all the time without ever tying up even one finger. You can play melody or riffs freely anywhere on the neck as long as they can be harmonized with any D family chord.
Drop D tuning is used almost exclusively to play in the key of D, or sometimes D minor. Even in these keys it has some drawbacks. The most obvious of these is the IV chord, or G. The tonic bass that props up the IV chord is on the sixth string, the string that has been retuned. That means that bass note has moved from the 3rd fret up to the 5th. While this is not insurmountable, it is inconvenient. Some of the things that fall easily under your fingers while playing a conventional G chord are either more difficult or not available in Drop D.
The key of D minor has some real problems. The drop chord, C, which is common in that key, loses access to its alternate bass on the sixth string. The contrast between the very strong I minor (Dm) chord and the weakened drop chord (C) is very evident.
All your full barre chords lose their bottom-string note in Drop D. Some of these, like F (feels like F, sounds like G) and Bb (C) are important chords in the D keys. Consider the common" E form" barre chord. In standard tuning it has a strong tonic bass on the sixth string. In Drop D it loses that.Now Look at the "Drop E" Partial Capo...
Instead of tuning the E string down a whole step, clamp the other 5 strings up a whole step. Finger a D shape chord, and you are so used to muting the low E string that it is easy to forget that you can play it as a six string chord, just as you would in Drop D tuning. It also has a low tonic root bass note on the bass E string, though of course it is a whole step higher than Drop D tuning. (If you were to capo 2 in Drop D tuning you would sound exactly like Drop E capo configuration.)
The open, unclamped sixth string is an E note. The D chord you're playing has been turned into an E by being capoed up a whole step. So you can play the D shape chord (actual pitch is E) as a full six-string chord with a nice open bass note on the sixth string, just like you would in Drop D tuning. So far there is no difference in sound between the tuning and the capo.
The big difference between tuning and capoing becomes clear when you play the G or IV chord. Unlike Drop D tuning, where the sixth string bass note for the IV chord is moved 2 frets by retuning, in Drop E partial capo configuration the IV chord plays normally. So does the Drop chord (play a C-chord just like always) in the minor key. So do all the barre chords. It has much of the same sound as Drop D tuning, but is easier to get used to, and you don't have to "trade away" as many regular features of your guitar landscape (like barre chords!) just to get that root bass on your D chord.
The Partial Capo "Trade-Off"...
As you might expect, a partial capo often involves a trade-off. You get a much richer 1 chord when you play in D position. but your 2 chord (either the F#m chord- you play Em fingering, or the F#7 where you play E7) loses it's usual open bass E string root. In some songs this is an important chord, and in thousands of others it doesn't show up at all. So you have traded a strong 1 chord for a weaker 2 chord.
Fortunately, if you are using a low profile open jaw capo (like a Shubb, Dunlop or G7) to clamp the Drop E, it isn't too difficult to reach over the capo to get that bass note back, or you can get a slick Kyser Lever capo with a push-button lever that frets that note that is under the capo at the 2nd fret. You might also decide this is the wrong way to arrange a song that relies too heavily on the 2 chord, though it is rare to find a song that needs a stronger 2 chord than a 1 chord.
Another big advantage of the Drop E capo configuration is that you can "cross-key" and play in G position. When you do this (actual pitch A), there are not trade-offs on your 3 basic 1-4-5 chords, and get a standard I chord, a standard IV chord, and a V chord with an extra tonic bass note on the sixth string. This is worth considering for almost any G position I-IV-V song. The fingerings are all familiar, but a vital chord in the key is noticably improved.Summary...
When you retune, all of the notes in your chords and scales move around on the fingerboard. The familiar fingerings of chords and scales are lost, and it is a big project to "re-learn" the fingerboard for each tuning..
Open tunings are good ways to discover musical combinations you might never find in standard tuning. Open tunings open new doors, but they also close others. Sometimes the doors that are opened are outnumbered by the disadvantages of the tuning. The same is true of the partial capo. It's not a replacement for re-tuning your guitar-- it is a "mirror-image" of the tuning world that offers a similar and equally-large new set of possibilities to any player, without the work of re-tuning and of re-learning the fingerboard.
Standard tuning probably offers the most versatility. You can play with relative convenience in many different keys using standard tuning. Non-standard tunings are much more specific. Usually they're effective in only one key. A particular tuning may give you a great I chord, a good IV chord, and an acceptable V chord, but perhaps no good way to finger a relative minor. This is why most players who use open tunings a lot, use a lot of different open tunings. Otherwise everything starts to sound the same.
Partial capoing only alters chords and scales where one of the unclamped strings is played open. Barre chords and closed-position scales are entirely unaffected. Many nut-position chords are fingered normally as well, depending on the configuration. A partial capo can give you access to open tuning-like tonalities, and to chord voicings not available in standard tuning, without turning your fingerboard into an unknown world.