down; whereas in the second couplet, in the word "Camilla" all the syllables are short, even the stressed one. The last line is in fact an alexandrine — an iambic hexameter, which occurs occasionally in some iambic pentameter texts as a variant line, most commonly the final line of a passage or stanza, and has a tendency, as in this example, to break in the middle, producing a symmetry, with its even number of syllables split into two halves, that contrasts with the asymmetry of the 5-beat pentameter line. Pope exemplifies "swiftness" partly through his use of contraction: two extra implied syllables squeezed into the metrical template between the first 2 ictuses:- / ×(×) (×)× / × / × / × / × / Flies o'er th'unbending corn, and skims along the main. Moreover, iambic pentameter, instead of the steady alternation of lighter and heavier beats of four-beat, permits principal accents, that is accents on the most significant words, to occur at various points in a line as long as they are on the even–numbered syllables, or on the first syllable, in the case of an initial trochaic inversion. It is not the case, as is often alleged, that iambic pentameter is "natural" to English; rather it is that iambic pentameter allows the varied intonations and pace natural to significant speech to be heard along with the regular meter. Theories of iambic pentameter Halle–Keyser Linguists Morris Halle and Samuel Jay Keyser developed the earliest theory of generative metrics — a set of rules that define those variations that are permissible (in their view) in English iambic pentameter. Essentially, the Halle–Keyser rules state that only "stress maximum" syllables are important in determining the meter. A stress maximum syllable is a stressed syllable surrounded on both sides by weak syllables in the same syntactic phrase and in the same verse line. In order to be a permissible line of iambic pentameter, no stress maxima can fall on a syllable that is designated as a weak syllable in the standard, unvaried iambic pentameter pattern. In the Donne line, the word God is not a maximum. That is because it is followed by a pause. Similarly the words you, mend, and bend are not maxima since they are each at the end of a line (as required for the rhyming of mend/bend and you/new.) Rewriting the Donne quatrain showing the stress maxima (denoted with