The most common simple sentence in modern English follows a familiar pattern: Subject (S), Verb (V), Object (O). To illustrate this, we'll devise a subject (John), a verb (caught), and an object (the ball). Thus, we have an easily understood sentence, "John caught the ball." This is as perfectly an understood sentence in modern English as it was in Shakespeare's day. However, Shakespeare was much more at liberty to switch these three basic componentsand did, quite frequently. Shakespeare used a great deal of SOV inversion, which renders the sentence as "John the ball caught." This order is commonly found in Germanic languages (moreso in subordinate clauses), from which English derives much of its syntactical foundation.1
Another reason for Shakespeare's utilization of this order may be more practical. The romance languages of Italian and French introduced rhymed verse; Anglo-Saxon poetry was based on rhythm, metrical stresses, and alliteration within lines rather than rhymed couplets. With the introduction of rhymed poetic forms into English literature (and, since the Norman invasion, an injection of French to boot), there was a subsequent shift in English poetry. To quote John Porter Houston, "Verbs in Old French and Italian make handy rimes, and they make even better ones in English because so many English verbs are monosyllabic. The verse line or couplet containing a subject near the beginning and a verb at the end is a natural development."2
Of course, Shakespeare wrote a great deal of work in blank verse (unrhymed iambic pentameter); when he wasn't rhyming, what was he thinking? Frankly, Elizabethans allowed for a lot more leeway in word order, and Shakespeare not only realized that, he took advantage of it. By utilizing inverted word orders, Shakespeare could effectively place the metrical stress wherever he needed it mostand English is heavily dependent on vocal inflection, which is not so easily translated into writing, to suggest emphasis and meaning. In his usage of order inversion, however, Shakespeare could compensate for this literary shortcoming.
Shakespeare also throws in many examples of OSV construction ("The ball John caught."). Shakespeare seems to use this colloquially in many places as a transitory device, bridging two sentences, to provide continuity. Shakespeare (and many other writers) may also have used this as a device to shift end emphasis to the verb of a clause. Also, another prevalent usage of inversion was the VS order shift ("caught John" instead of "John caught"), which seems primarily a stylistic choice that further belies the Germanic root of modern English.
In the end, Houston points to "the effort to make language more memorable by deviation from spoken habits."3 This is the essence of poetry: a heightening of language (even colloquial) above that of prose, a heightening that produces an idealized, imaginative conception of the subject.
1 There is no argument that English contains less than a fair share of French and Latinate words in its vocabulary; of course it does, which one would expect given the 1066 invasion of William the Conqueror (from Normandy, in France). But, as a linguistics professor once put it, "Think of the English language like a house: the decor is French, but the foundation and frame is Germanic." Fortunately, we decided to drop a couple of pronoun cases and the gender-specific articles by the time we get to modern English.
2 John Porter Houston, Shakespearean Sentences: A Study in Style and Syntax (LSU Press, Baton Rouge, 1988), 2
3 Ibid, 20. The fine line of dramatic poetry is that ability to deviate from spoken habits enough to make it memorable, yet still keep the language within the constraints imposed by story, plot, and character. A play, even done in verse, is a different animal from the art of poetry.