Comma titles that follow a name: "John Smith, Ph.D." Similarly in lists that are presented with an inversion: "...; socks, green: 3 pairs; socks, red: 2 pairs; tie, regimental: 1". Commas may be used to indicate that a word, or a group of words, has been omitted, as in "The cat was white; the dog, brown." (Here the comma replaces "was".) Commas are placed before, after, or around a noun or pronoun used independently in speaking to some person, place or thing: In his 1785 essay "An Essay on Punctuation", Joseph Robertson advocated a comma between the subject and predicate of
Colon (punctuation) Colon (punctuation) The colon ( : ) is a punctuation mark consisting of two equally sized dots centered on the same vertical line. A colon precedes an explanation or an enumeration, or list. A colon is also used with ratios, titles and subtitles of books, city and publisher in bibliographies, Biblical citations between chapter and verse, and for salutations business letters and other formal letter writing, and often to separate hours and minutes. The most common use of the colon is to inform the reader that what follows the colon proves, explains, defines, describes, or lists elements of what preceded