Music for Strings, Percussion and Celesta (1936) and Divertimento for String Orchestra (1939) belong to those charismatic works by Béla Bartók (1881-1945) that probably best embody the Hungarian composer's contribution to the music of the 20th century. They make up a unique pair. Both are very personal messages from a turbulent decade when his two greatest contemporaries, Schoenberg and Stravinsky, had already left Europe. The one - the Music for Strings, Percussion and Celesta - is often and justly called Bartók's chef-d'oeuvre, written in an entirely personal idiom, a deeply Hungarian yet universally comprehensible musical language, at once sublime, at once magically pagan in tone. It is a four-movement piece with perfect proportions, with sensational tirnbres and stereophonic effects between the corps of the orchestra. The other - the Divertimento for String Orchestra - consists of three movements and is purely for strings, a conceivably less attractive but in fact emotionally more direct communication unmistakably revealing Bartók's exuberant feelings just before World War II broke out. He worked on the draft score between 2-17 August 1939, postponing the composition of the slow middle movement, the darkest vision, until the end of the very intensive period. In both cases, Bartók avoided using the title “symphony". For the first work, he suggested a French title, "Musique pour instruments à cordes, batterie et célesta, en 4 mouvements"; for the second his preliminary title was "Werk/Suite? für Streichorchester", which he turned to Divertimento when the draft score was finished.
As is generally known, both scores were commissioned and premiered by Paul Sacher and his Basle Chamber Orchestra, a well-trained group that, nevertheless, included non-professional instrumentalists, a fact that did not disturb Bartók at all. Lesser known is that he was already working on a new composition, the proto-form of Music for Strings, Percussion and Celesta, when Sacher's letter reached him. Originally Bartók was thinking of a piece for string chamber orchestra alone. The opening Andante tranquillo fugue was finished in a five-part string setting before, from the second movement on, he switched to the double string orchestra plus percussion concept. (A study ofthe facsimile of the autograph score kept in the Paul Sacher Stiftung, edited by Felix Meyer, Schott 2000, offers  an exceptional experience.)
Another peculiarity of the acoustic concept of Music is the precise seating plan as Bartók defined it. It is generally ignored, however, because it was incorrectly printed in the score (see the enclosed facsimile of the plan in Bartók's handwriting; NB Maestro Harnoncourt follows faithfully the cornposer’s concept and makes the most of it). Bartók positioned the extra instruments on an axis, thus dividing the left-hand and right-hand string orchestras, with the timpani presiding at the top and the piano at the bottom of the "line of demarcation." This special stereophonic conception of the score, which goes beyond the acoustics and is part of the semantics of the music, requires not only left-hand and right-hand partners in an antiphonal dialogue, but also a center from where the quasi judgment comes at major articulation points of the form.
The concept of Music with its slow-fast-slow-fast four-movement design signaled a breakthrough in Bartók's middle period. After the famous five-movement or five-part symmetrical instrumental works with recurring themes in the first and last and in the second and fourth parts (String Quartets Nos. 4 and 5, Piano Concerto No. 2), here four independent pieces make up the form: nevertheless, variants of the initial pianissimo fugue theme do reappear in the subsequent movements. This theme creates the shrill ostinato in the center of the sonata-form Allegro second movement; its phrases separate the A-B-C-B-A sections of the bridge-form Adagio; finally, extending the chromatic theme into a diatonic version, it gives voice to the hymn-like molto espressivo in the coda of the Allegro molto finale. Far beyond the network of thematic links and other features of strict planning - including a key plan that uses tritone relations (a workin A, with E flat peak in the first movement; the second and third movements in C and F sharp, respectively) -, each movement is an individual masterpiece. And each of the basic themes, without actual borrowing, is deeply rooted in Hungarian folk music: e.g., the four-line stanza contour of the fugue theme and its dance-tune variant as the opening theme of the second movement; the rhythm and the ornaments of the Adagio theme; the finale as a whole, including children’s play song imitations.
Planning the Divertimento, months before the actual composition started - which usually happened between the instrument and the desk: improvising at the piano and writing the draft score -, Bartók notified Paul Sacher: "I have the idea... of a kind of concerto grosso alternating with concertino" (1 July 1939). After Sacher assured him that adequate players would be available, Bartók, for the first time, adopted this neo-baroque texture in his not at all “neo”-style composition. Incidentally the number of instrumentalists as given in the score (at least 6, 6, 4, 4, 2 players) corresponded to the regular size of the Basle Chamber Orchestra but Bartók preferred a larger body: "a complete string orchestra is naturally even more suitable." (Harnoncourt’s balance gives proof of his perfect understanding of Bartók’s intentions. Besides, having great respect forthe Hungarian string playing traditions, Nikolaus Harnoncourt achieves wonders in coaching a Bartók style, which may be called unique today, to young musicians.)
The opening theme of the sonata-form Allegro non troppo, in the key and meter of baroque pastoral pieces (9/8 in F), but truly in Hungarian dance-style, is followed by a series of contrasting themes, reminding one of the wealth of Mozart’s expositions. The Allegro assai finale is based on the 2/4 overt dance variants of the same themes, in their elaboration implying tones of the ironic and humorous, such as pedantic counterpoint, Gipsy rubato, and a tipsy episode (a polka) before the end. The Molto adagio middle movement belongs to Bartók's night music topos: a sorrowful violin melody followed by a Hungarian lament, then cries and shouts, with a return to the extremely expressive chromatic melody - one of the most moving pieces he was ever to write.