Note: All pictures shown on slides 1,2, and 3 of this online guide were retrieved from the RBI Digital Collection found at this link: https://digital.opal-libraries.org/digital/collection/p16708coll9/id/52/rec/1
The instrumentation in Così Fan Tutte contains Violin, Viola, Oboe, Flute, Horn, Vocalists, and Bass. Mainly in this piece the violins have the melody where violin one will play some interesting rhythms that are combatted by violin two playing repeated eighth notes or varying rhythms that hold the reins for violin one. Oboe, bass, and viola are paired to sustain the harmony of the piece and they work with the melody to create something beautiful.
The flutes and horns are paired also to hold the harmony and contrasts, but they also switch between playing a harmonic set of lines and playing a melodic set of lines, which I think is a great way to show off those instruments. Once the vocalists enter, the horn, flute, and oboe parts are less used, while the violins, viola, and bass are still used with ever increasing rhythmic difficulty. Overall, the rhythmic ideas that are specific to each part are intriguing and exciting to see if you read and listen along to piece.