were W.K. Wimsatt & Monroe Beardsley the first to use multiple slashes: none other than Thomas Jefferson used a 5-level notational system of accents ("////" for strongest stress, down to "/" for little stress, and no mark for "no" stress). Steele and McAuley have used Jespersen's 4-level notation as a secondary method. Wimsatt, Woods, and The New Princeton Encyclopedia of Poetry and Poetics have used Chomsky & Halle's notation as a secondary method. One of the primary virtues of 4-level scansion is that it helps clarify a surprisingly specific—and surprisingly controversial—debate. Take the rhythmically complex line: When to the sessions of sweet silent thought Some prosodists hear "-ions of sweet si-" as a very light iamb, followed by a very heavy iamb, yielding a 2-level metrical scansion of: / × × / × / × / × / When to the sess | ions of sweet si | lent thought ("Foot" markers are used here merely to emphasize the syllables in question. Recall that this metrical scansion does not imply that "of" is necessarily spoken with more emphasis than "sweet", only that these fill ictic and nonictic positions, respectively.) However, other prosodists hold that, just as the usual 2nd position ictus has been switched to 1st position, so the usual 6th position ictus has been switched to 7th, yielding: / × × / × × / / × / When to the sess | ions of sweet si | lent thought In this case, "-ions of sweet si-" is sometimes taken as a pyrrhic foot followed by a spondee, and sometimes as a single 4-syllable unit (a minor or rising ionic) that replaces 2 iambic feet. This is a case in which 2-level scansion is felt to miss something essential even by some rather strict prosodists. In fact, Groves has shown that in cases like this, where the ictus moves forward (as opposed to backward as in "When to") each of the 4 positions in question has slightly different constraints that must be fulfilled for the line to be perceived as metrical. In layman's terms, these constraints are most often realized as 4 rising positions; in Jespersen's notation: 3 2 1 4 1 2 3 4 1 4 When to the sess | ions of sweet si | lent thought In this case, everyone is somewhat right: the 4 positions are like a light then a heavy iamb, and like