English in the 15th through 17th centuries included a growth in the use of such abbreviations. At first, abbreviations were sometimes represented with various suspension signs, not only periods. For example, sequences like ‹er› were replaced with ‹ɔ›, as in ‹mastɔ› for master and ‹exacɔbate› for exacerbate. While this may seem trivial, it was symptomatic of an attempt by people manually reproducing academic texts to reduce the copy time. In the Early Modern English period, between the 15th and 17th centuries, the thorn was used for th, as in ('the'). In modern times, was often used (in the form ) for promotional reasons, as in . During the growth of philological linguistic theory in academic Britain, abbreviating became very fashionable. Likewise, a century earlier in Boston, a fad of abbreviation started that swept the United States, with the globally popular term OK generally credited as a remnant of its influence. Over the years, however, the lack of convention in some style guides has made it difficult to determine which two-word abbreviations should be abbreviated with periods and which should not. This question is considered below. Widespread use of electronic communication through mobile phones and the Internet during the 1990s led to a marked rise in colloquial abbreviation. This was due largely to increasing popularity of textual communication services such as instant and text messaging. The original SMS supported message lengths of 160 characters at most (using the GSM 03.38 character set), for instance. This brevity gave rise to an informal abbreviation scheme sometimes called Textese, with which 10% or more of the words in a typical SMS message are abbreviated. More recently Twitter, a popular social networking service, began driving abbreviation use with 140 character message limits. Style conventions in English In modern English, there are several conventions for abbreviations, and the choice may be confusing. The only rule universally accepted is that one should be consistent, and to make this easier, publishers express their preferences in a style guide. Some questions which arise are shown below. Lowercase letters If the original word was capitalized then the first letter of its abbreviation should retain the capital, for example Lev. for Leviticus. When a word is abbreviated to more than a single letter and was originally spelled with lower case letters then there is no need for capitalization. However, when abbreviating a phrase where only the first letter of each word