Agostino Agazzari (1578-1640) wrote important views about continuo practice in early Italian baroque music in his book 'Del sonare sopra il basso' 1607. The text is very, very useful also today!
Oliver Strunk published English edition in 1952 in his 'Source Readings in Music History'. My quotes are from his book.
[Comment in 30 March 2004: There is an excellent version of Agazzari's article by Bernhard Lang in the Werner Icking Music Archive! All the text is in Italian, English and German!]
I quote and comment some parts, which I consider important for us, who are learning the early basso continuo tradition. My own comments inside the text are between '[' and ']'. The headers are mine.
So lute, theorbo and harp are suitable in both roles! Also, it is expected that there are 'ornament' instrumets, which play 'contrapuntal fashion' and make the harmony 'more agreeable and sonorous'. This means orchestral improvisation! More of this later.
There is not much to add! Agazzari's addition in parantheses is worth of noting. Already practical understanding of counterpoint may be enough 'at least'. Understanding voice leadings from dissonance to consonance and the nature of 3ths and 6th are important.
So here we can see how Agazzari belongs to the 'seconda prattica' group. The text to be sung defines the affect and the harmony depends on that, not on some abstract compositional procedures! And what follows says that even stronger:
"And even though some writers who treat of counterpoint have defined the order of progression from one consonance to another as though there were but one way, they are in the wrong; they will pardon me for saying this, for they show that they have not understood that the consonances and the harmony as a whole are subject and subordinate to the words, and not vice versa, and this I shall defend, if need be, with all the reasons I can."
One important matter to be taken into account is, I think, that also applying LATER practices to the continuo of early baroque may lead to inappropriate solutions. The importance of text clearly diminished later; Bach and Handel for example wrote their arias quite 'instrumentally' compared to the style of early monodists.
"Since all cadences [!] , whether medial or final, require the major third [!], some musicians do not indicate it; to be on the safe side, however, I advise writing the accidental, especially in medial cadences."
And also later in the book:
"... I take for granted certain number of principles ... cadences require the major third, ..."
I made a small 'researh' of the type of cadences in Italian baroque lute music.
"...I say the same [as he said above about the organ] of the lute, harp, theorbo, harpsichord, etc., when they serve as foundation with one or more voices singing above them, for in this case, to support the voice, they must maintain a solid, sonorous, sustained harmony, playing now piano, now forte, according to the quality and quantity of the voices, the place, and the work, while, to avoid interfering with the singer, they must not restrike the strings too often, when he executes a passage or expresses a passion."
This is very important paragraph!
"... these must make the melody flourishing and graceful, each according to its quality, with a variety of beautiful counterpoints. ... the instruments in the first class [foundation] ... require no great knowledge of counterpoint in the player, the second class [ornament] do require it, for the player must compose new parts above the bass and new and varied passages and counterpoints."
I just wonder, why this practice is not flourishing nowadays. We have had Agazzari's text already 388 years! What happened to the music? What diminished the role of the musician in favor of the composer hero?
I personally remember the joy and freedom, when I started continuo playing (well, some years after starting, starting is not so easy and not always joyful!). After having played 'ready made' pieces just as written, it was really something to be requested and allowed to make your own music! It somehow reminded me of the school days, when we had a blues band (not very good one, but anyway, we improvised).
"Sometimes, therefore, he must use gentle strokes and repercussions, sometimes slow passages, sometimes rapid and repeated ones, sometimes something played on the bass strings, sometimes beautiful vyings and conceits, repeating and bringing out these figures at different pitches and in different places; he must in short, so weave the voices together with long groups, trills and accents, each in its turn, that he gives grace to the consort and enjoyment and delight to the listeners, judiciously preventing these embellishments from conflicting with one another and allowing time to each, especially when there are other similar instruments, a thing to be avoided, in my opinion, unless they play at great distance or are differently tuned or of different sizes."
The variety seems to be the key word! As I concluded my ' Basics of the basics of lute continuo', only sky is the limit! And expressing the text is always there; also the variety must serve the text! Playing "runs and divisions from beginning to the end" doesn't serve any text.
And also here is the warning of conflicting; it is not enough to listen to the singer(-s), but you must hear and react to everything there happens.
"But since each instrument has its own peculiar limitations, the player must take the advantage [!!] of them and be guided by them to produce a good result."
I think this is very important, even a philosophical remark. Limitations are not really limitations, they are possibilities, advantages, for expression!
This reminds me of the difference between studying modern and historical instruments: for example modern pianists and guitarists try to overcome the different lengths and strengths of their fingers, lutenists and harpsihordists take full advantage of the differences: strong notes are played with strong fingers, weak with weak fingers.
I just ask, which way is more natural?
"The player of lirone must bow with long, clear sonorous strokes, ... The violin requires beautiful passages, distinct and long, with playful figures and little echoes and imitations repeated in several places, passionate accents, mute strokes of the bow, groups, trills, etc. The violone ... proceeds with gravity ... The theorbo, with its full and gentle consonances, reinforces the melody greatly, restriking and lightly passing over the bass strings, its special excellence, with trills and mute accents played with left hand. The arpa doppia, which is everywhere useful, as much so in the soprano as in the bass, explores its entire range with gentle plucked notes, echoes of the two hands, trills, etc.; in short, it aims good counterpoint."
"... if the instruments are alone in the consort, they must lead it and do everything; if they play in company, each must regard the other, giving it room and not conflicting with it; if there are many, they must each await their turn and not, chirping like sparrows, try to shout one another down. Let these few remarks serve to give some light to him, who seeks to learn."
Isn't it nice that there is no limit in what you can learn, even if you would play only music composed in 1600-1610!