By

By is a common preposition in English with a range of functions. It can indicate location or proximity, as in a house by the river; it can mark the agent in a passive construction, as in The novel was written by Jane Austen; and it can signal the instrument or means by which something is done, as in written by hand or sent by email. It also covers time expressions and deadlines, as in finish by Friday or arrive by noon, and appears in measurements and dimensions, for example a 3 by 5 foot table or a photo described as 4 by 6 inches.

Beyond these, by can denote route or mode of travel (go by train), establish close association or contrast (by contrast, by and large), and form common idioms and collocations such as by the way, by all accounts, or by means of. It is also used to attribute authorship or creation, as in a painting by Picasso or a song by Bob Dylan, and to indicate a basis for evaluation or change (increase by ten percent).

Etymology and related usage: By descends from Old English bi, be, with cognates in other Germanic languages such as Dutch bij and German bei, reflecting enduring uses related to proximity, agency, and method. The word remains highly productive in modern English, including fixed phrases and phrasal verbs such as stand by, go by, and by agreement.

Other notes: In uppercase form, BY serves as the ISO 3166-1 alpha-2 country code for Belarus and appears in the country domain .by. By can also function as part of a byline, indicating the author of a work.