Tsukesage, which is written as '付け下げ' or '付下げ' (pronunciation is the same), is kimono for Japanese women.
Issue whether tsukesage is a formal dress or not
Tsukesage has characteristics that it doesn't have eba-moyo (or 'eba') nor kamon (crest), and its hakkake (inside cloth used around cuff and hem) is not tomosuso (made of the same plain cloth as the front). Eba-moyo is the patterns which were drawn with special technique so that the patterns don't lose the figures at sewing points (back, side, and collar). If patterns lose the figures at sewing points, it is not called eba-moyo.
Formal dress is supposed to have eba-moyo, kamon, and susomawashi (hakkake) of mukujitate (sometimes mukujitate is called 'tomosuso'). Therefore tsukesage is supposed to be ranked formal dress and casual wear. In the early twentieth century, based on the technique of drawing komon (small patterns drawn on the whole cloth) craftsmen introduced new technique of drawing a little bigger pattern on materials so that patterns don't lose the direction. Due to the technique, more gorgeous patterns than komon began to be drawn on kimono. Such kimonos used the technique were called tsukesage.
Basically current tsukesage is not supposed to be a formal dress because of the lack of eba-moyo and kamon. However, some tsukesage with extremely gorgeous patterns might be regarded as a formal dress ranked next to normal homongi (formal kimono) such as tomesode (black formal kimono with kamon for married women).
Tsukesage with classical patterns is ranked over homongi with light patterns in some cases, so the difference between homongi and tsukesage tends to be gradually reduced
At first tsukesage was much simpler than homongi. Later fancy patterns began to be drawn on tsukesage.
In the sales style of kimono in which kimono is made after taking customer's order, tsukesage is sold in the form of tanmono (a roll of cloth for one kimono, patterns are already drawn on it) just like komon. In the old days, salespersons of kimono promoted the sales of tsukesage as a substitute for homongi. This is because tsukesage, which is sold by the roll, is less expensive than a formal kimono with an ebamono design (where the pattern spreads over the kimono without its alignment being disrupted by the seams) so it would be easier to sell to customers. It should be noted that the sales staff wanted customers who could not afford to buy a formal kimono to purchase tsukesage instead because, depending on the degree of formality required, it could be used as a substitute for a formal kimono.
Some people say that since the authority of fascism suppressed the production of homongi, people of the working class unwillingly invented tsukesage as a substitute for homongi; however that opinion is questionable.