As the examples show, iambic pentameter need not consist entirely of iambs, nor need it have ten syllables. Most poets who have a great facility for iambic pentameter frequently vary the rhythm of their poetry as Donne and Shakespeare do in the examples, both to create a more interesting overall rhythm and to highlight important thematic elements. In fact, the skillful "variation" of iambic pentameter, rather than the consistent use of it, may well be what distinguishes the rhythmic artistry of Donne, Shakespeare, Milton, and the 20th century sonneteer Edna St. Vincent Millay.