How to play the strange thing called a harpsichord effectively? There are many tricks that people use...
This means, roughly, what you do at the beginning of each note. Usually, one positions the hands facing forwards, palms horizontal and an inch or two above the keys, the fingers curling downwards to meet the keys, and thumbs slightly bent so that the last joint faces forwards. To activate the 'plucking' mechanism takes a certain amount of force; combine this with the fact that a single key may be plucking more than one string (if the harpsichord has many registers or manuals - like using different keyboards and sets of pipes on an organ), and you can work out that if the key is pressed too timidly you will get an untidy start to the note. So it's not possible to fade away into nothing, as you might try to on the piano or clavichord. Going the other way and using maximum force is not desirable either, since the dynamic range you can achieve is pretty small and the extra energy goes into making an ugly thud as the key hits its bed. A good general rule is not to move the hand about: the force should come from the fingers, not from elbow-grease. In contrast to piano-playing, there is no need to hit the keys from above: you can start with the fingers touching the keys before each note.
This means, roughly, the point at which you choose to end
each note. The quills have to slide back over the string to get back to the original position, which makes a certain noise at the end of the note (even though the string is damped). The way that this noise interacts with the following note can produce interesting effects. There are many varieties of articulation...
Staccato: meaning, there is a definite space between one note and the next. Usually, the shorter the staccato, the 'lighter' and less important a note sounds. This is an important element of Baroque performance, since the different beats within a single bar are traditionally accorded different 'strengths'. For example, in a four-beat bar, the first beat is taken to be the strongest, the third somewhat weaker and the 2nd and 4th weakest. The main way to differentiate them on a harpsichord is by using different degrees of staccato. If there is a syncopation or unusual melodic line contradicting the normal pattern of strong and weak beats, an intelligent use of staccato will help to express the unusual rhythm. Staccato can be appropriate in fast movements to create an effect of briskness and athleticism. Finally, staccato can actually emphasize an isolated note, if it interrupts an otherwise smooth legato run.
Staccato-legato, or staccato-cantabile: this is a sort of compromise articulation, meaning that each note is released infinitesimally before the next begins, resulting in a clean movement from one to the other without any actual silence. The little noise of the quills doing their stuff in between the notes acts a bit like the consonants in singing. This is the default articulation, the jumping-off point from which one can make expressive forays in the staccato or legato direction.
J.S. Bach's articulation: based on contemporary accounts, what he did was to gradually retract the finger towards the edge of the key and slide off it. This was supposed to make runs (fast series of notes) clearer. The resulting sound might have been like staccato-cantabile, or legato - it's difficult to judge exactly. Clearly, dealing with the end of the note was at least as important as the beginning. (Also, we should not assume that he played every note like this!)
Legato: This means releasing one note just as the next one begins. This is usually what is wanted if the composer puts a slur marking over a group of notes. (But see the next paragraph.) The effect is to 'bracket' several notes together as a single gesture, like singing several notes on the same syllable. If used continually, legato can become boring and featureless, since it doesn't really add anything to the notes.
Überlegato, or over-legato: this does not mean a technique used by Nazi musicians, rather it is sustaining a note beyond its legally allowed time, so that it overlaps the following note. This can also be used, if the composer wrote a slur, usually on the first note of the group. The effect is to further strengthen the note and thicken the harmonic texture; the following note sounds weaker by contrast. Hence überlegato can be appropriate for suspensions or appoggiaturas, in which a strong dissonant note resolves smoothly onto a weak note with a 'sighing' effect. Another use for überlegato is to sustain the harmonically important notes within a group, so that a chord is created althouth there is only a single melodic line in the score. Sometimes a composer will explicitly notate this effect.
Style brisée: this is not a French way of cooking, rather it is a phrase describing another technique of sustaining notes for longer than they are written. It can be appropriate if the melodic lines consists mainly of the notes of a chord: all the melody notes belonging to the chord are sustained until the harmony changes. This way of playing evolved out of the practice of improvising on a series of chords by playing arpeggios up and down. The most famous example is the Prelude no.1 in C major of J.S. Bach from the Well-tempered Keyboard Book 1, in which some of the sustained notes are actually written out. However, not all melodies consisting of broken chords should be sustained in this way, since it has a leisurely, meditative effect which would not be
appropriate in fast movements (e.g. Bach's two-part Invention in F major).
In general, Baroque music has been hurt by rigid and machine-like articulation more than by almost anything else. Both an unvaryingly smooth legato and an unvaryingly sprightly staccato very quickly lead to boredom. Alternating between the two will not help much, either, despite the resulting violent contrast! The ideals for me are subtlety, flexibility, naturalness, and responsiveness to the structure and expression of the music.
This is a huge subject, and I won't be able to do more than indicate some of the most common tricks.
First, 'breaking' or 'rolling' of chords: essentially, playing notes that are written to sound together at slightly different times. With a chord of several notes, you have the choice to break upwards or downwards, fast, slow, accelerating, decelerating, etc. This vastly increases the range of sounds you can obtain. If the music consists of just a few parts, breaking is less effective; in any case, it tends to obscure any counterpoint that the composer has written, since it puts the emphasis on notes as making up a chord ('vertical' organization), rather than as forming part of an independent line or voice ('horizontal' organization). It takes some skill to keep a steady beat going when you have big broken chords: does the beat come at the beginning or the end of the roll? In contrast to romantic music, Baroque music usually works with the first note of the broken chord on the beat, but there are no hard rules about it.
Some harpsichordists like to break even when there are only two notes to be played together. This has the effect of emphasizing the melody (assuming that the upper note is played later) but ultimately becomes tiresome since it 'flattens' and obscures any contrapuntal structure.
Notes inégales are another French term, meaning playing the first out of each group of two notes longer (or, occasionally, shorter) than the second by some carefully-judged amount. This can be either very expressive or very annoying, depending on how it is carried out. Naturally it only makes sense for passages which fall into groups of two notes. Attempts to play Bach with notes inégales are usually unsuccessful: the technique belongs mainly to French Baroque music.