What's the difference between Classical Chinese and Modern Chinese?
The following is an excerpt from wikipedia, Classical Chinese Grammar:


  Grammar
  
  Further information: Classical Chinese lexicon
  
  Classical Chinese is distinguished from written vernacular Chinese in
  its style, which appears extremely concise and compact to modern
  Chinese speakers, and to some extent in the use of different lexical
  items (vocabulary).[citation needed] An essay in Classical Chinese,
  for example, might use half as many Chinese characters as in
  vernacular Chinese to relate the same content.
  
  In terms of conciseness and compactness, Classical Chinese rarely uses
  words composed of two Chinese characters; nearly all words are of one
  syllable only. This stands directly in contrast with modern Chinese
  dialects, in which two-syllable words are extremely common. This
  phenomenon exists, in part, because polysyllabic words evolved in
  Chinese to disambiguate homophones that result from sound changes.
  Similarly, Chinese has acquired many polysyllabic words in order to
  disambiguate monosyllabic words that sounded different in earlier
  forms of Chinese but identical in one region or another during later
  periods. Because Classical Chinese is based on the literary examples
  of ancient Chinese literature, it has almost none of the two-syllable
  words present in modern Chinese languages.
  
  Pronouns
  
  Classical Chinese has more pronouns compared to the modern vernacular.
  In particular, whereas Mandarin has one general character to refer to
  the first-person pronoun ("I"/"me"), Literary Chinese has several,
  many of which are used as part of honorific language (see Chinese
  honorifics), and several of which have different grammatical uses
  (first-person collective, first-person possessive, etc.).[citation
  needed]
  
  Syntax
  
  In syntax, Classical Chinese is always ready to drop subjects, verbs,
  objects, etc. when their meaning is understood (pragmatically
  inferable). Also, words are not restrictively categorized into parts
  of speech: nouns used as verbs, adjectives used as nouns, and so on.
  There is no copula in Classical Chinese, "是" (pinyin: shì) is a copula
  in modern Chinese but in old Chinese it was originally a near
  demonstrative ("this"); the modern Chinese for "this" is "這" (pinyin:
  zhè).
  
  Word order
  
  The Classical Chinese word order is often the reverse of Mandarin; for
  example, Mandarin 饒恕 (pinyin: ráoshù, "forgive") is Classical 恕饒
  (Classical Chinese: ŋjew hnjas).1 [2]