The principal classification scheme for manuscripts held by Houghton Library is by language or country/culture, but some manuscripts are classified by subject/genre (MS Mus[ic]), by collector (MS Richardson), or by library department (MS Typ for manuscripts in the Department of Printing and Graphic Arts).
Anything “owned” by the Harvard Theatre Collection or the Department of Printing and Graphic Arts, regardless of language, culture, or medium, will be classed as MS Thr or MS Typ, respectively.
For items not under the auspices of HTC or P&GA, consider what is the primary element of the material. Materials that are primarily musical scores will be MS Mus. Materials that are ½ musical scores and ½ literary work may be classified by language or culture. American (U.S.) and British materials, regardless of language, are mostly likely to be classed in MS Am and MS Eng, respectively.
This cultural primacy is not as clear in some of the other language/culture classifications. Most often with materials not related to the U.S. or Great Britain, language trumps culture, so that an item written in French about Spain is more likely to be in MS Fr than MS Span. There are many instances when this is not the case and often the decision for such exceptions comes down from a curator or is at the cataloger’s discretion. For example, if this French-language item is the story of travels through Spain by a French citizen, it would almost definitely be classed as MS Fr; if it were a French translation of a Spanish legal or government document, it would probably be classed as MS Span; if it were a French language account of the Spanish Civil War, it could be either MS Fr or MS Span. When in doubt, consult the curator.
Note that MS Eng is used both for British materials and for materials written in English concerning any country or culture, except the United States (MS Am). MS Eng is both a language and a cultural designation.
A closed classification does not preclude adding to this classification if appropriate materials are discovered or need further cataloging; it is simply that materials for these classifications are not actively sought.