In the last part of the 20th century a great debate started - which still continues - on the question of whether the best performance or the most adequate, o even the only possible one, is the nearest to an "authentic" performance, this is to say, to the hypothetical performance that the creators and contemporary performers of that music would do (and did do); this way of thinking has created a manner of performance called: period instruments performance, or historical performance, or historically informed performance (HIP), and in turn, this has produced a rejection from the performers more attached to the tradition, but no doubt has influenced their ways of performance. What we exactly mean by more attached to the tradition, is referring to the great performing tradition transmitted uninterruptly from masters to pupils since the 19th century (but not before, because then usually no one performed music of earlier times).
From this new performing fashion came the recent recovery of period instruments to perform early music (a few may be originals, but the majority are replicas), as well as the study of each musical period and the conventions that constitute the style.
A very important guide to achieve a historically informed performance is the one provided by the study of the contemporary texts of each epoch which describe the performing manner of their time, and within it, the styles of each country or region. But we have to take into account the fact that the practical musician is always ahead of the theoreticians, and when these ones decide to write a code of the present performing practice, this is already about to start changing into a newer thing.
To judge the music theory texts, we need to have into account that the ones from the Middle Ages are in fact theological philosophical writtings which use music for their philosophical reflections, while the Renaissance and Baroque texts try to link music to the classical greek thought (and justify it thereby), and it is not until the end of the 17th and specially the 18th century that the treatises begin to content more practical performing indications. Next, we will have a more detailed look at these historical periods.