Isochrony arises in nature, whether in the form of successive sunrises, cave-drips or heartbeats. AS does not. It is an active mental projection, allowing us to perceive and measure the passing of time through the metrical divisions of binary groups.
AS is projected into the tactus of our speech when the isochronic distribution of strong stresses becomes exaggerated enough to be plainly heard. These occasions are ‘emotional speech acts’, which are both imitated and invoked under poetic conditions. Often we find the isochronic effect also overdetermined by metre. As well as binary units like iambs and trochees, our syllables can also be arranged in ternary units, such as triple metres – a happy possibility, helped by several factors: the longer length of s-stressed syllables, and their easy isochronic alternation with two weak syllables; and the grammatical alternation of strong-stress content and weak-stress function words (added to the fact that there are generally more of the latter in any typical speech act).1
As know from the tick-tock effect, AS is hierarchical, which is to say that once established, groups of strong-weak-strong-weak beats will form larger units where the s-w alternation between them is still maintained. Thus strong-weak-strong-weak is heard as STRONG-weak-strong-weak; STRONG-weak-strong-weak-STRONG-weak-strong-weak is soon heard as STRONG-weak-strong-weak-STRONG-weak-strong-weak, and so on. Ternary groups are non-hierarchical, and such is the immense AS pull of the duple, they have a strong tendency to resolve themselves as binary at the next level up, if they possibly can. Musicians will know that a 3/4 time signature strongly resolves into two-bar measures, and does not propose three-bar cycles; if one uses melody or repetition to overdetermine a 3 × 3/4 = 9/4 time signature, it will then strongly pull to a longer two-bar measure of 2 × 9/4; ditto 3 × 9/4, which will pull towards a long binary strophe. The AS binary is simply a cognitive frame we find impossible to kick, and arises instinctively as soon as there is no overdetermining frame to prevent it from doing so. A point to bear in mind is that the binary is countable at all these various levels only because it maintains the natural asymmetry it possesses at the smallest level – in our case, the syllabic – through every larger unit. Larger s-w binary strophes not built up from low-level metrical AS are certainly possible, but they are not particularly strongly felt.
We have a distinct preference for AS in our word-combinations, and the so-called ‘rhythm rule’ shows the ASR is observed wherever it can be. The stress in a word will often shift in order to avoid consecutive, non-alternating stresses: thus GlenCOE, but GLENcoe MASSacre; FIFteen WINdows, but the FIRST fifTEEN. AS enters non-phrasemic speech too: unSAFE, but UNsafe STRUCTure; at a university council meeting the other day I heard, in a single sentence, both inSANE iDEA, and INsane POLicy. Words are generally keen to shape themselves to alternating pattern; while the lexical prosody of many bisyllabic and polysyllabic words is relatively fixed, w stress monosyllabic function words and functional affixes are often cheerfully enlisted as free agents for ‘promotion’ when the metrical context requires them to step up – and s stress content words and lexemes will take a demoted back seat when asked to.
Polysyllabic words which contain consecutive weak stresses will often allow one of them to be promoted. Thus ‘American’ is generally spoken x/xx; but in an iambic frame – ‘Americans are mostly English-speaking’ – the third syllable is felt, marginally, as a secondary s stress, allowing us to scan it in its metrical context as x/x/. (Frames have to be held in the mind before the words are spoken to exert any influence over their prosody.) ‘Words have one strong stress, and if you hear two, it’s two words’ is still a good general rule to hold by, though polysyllabic words do have light secondary s stresses. These are often heavily exaggerated under metrical circumstances when the ASR requires them to be; but this phenomenon has led some prosodists to reify secondary s stress, and talk as if its presence in real speech – as opposed to its performance within metrically overdetermined lines – is far greater than it really is, to the extent of marking secondary s stress in lexical stress analysis.
Some generative theorists hold that AS is so powerful, the spondee is impossible, since one stress will always incline to be the weaker. I doubt this is true. A more reliable rule is that whenever we encounter three consecutive s stresses bounded by w stresses, the middle one will weaken to maintain the alternate pattern; with three w stresses bounded by s stresses, the middle will strengthen. (I’ll discuss this in detail later.) It would to more reasonable to say that two consecutive s stresses are unstable, and are more likely to adapt to their metrical, semantic or contextual circumstances through one of them weakening, or through the interpolation of a weak-substitute mora; but there is no logical reason why they should not also occasionally defy the ASR for much the same reasons.
As mentioned previously, monosyllabic content words tend to take a strong stress, monosyllabic function words, a weak. Often the w stress part of bisyllabic or polysyllabic words is a functional affix. Thus the underlying, alternating pattern of isochronic English is not just between weak and strong, but between function and content (i.e. between grammatical and lexical function, and so between the universal forces of the syntagmatic and paradigmatic). Strong stresses tend to foreground lexis, weak stresses tend to background grammar; imposing a regular strong-weak alternation will therefore reinforce this arrangement. In metrical English, more s stress is introjected than in normal conversational English, and this gives the strong psychological impression that poetic language is relatively content-heavy, ‘dense with information’ – one of several factors that account for its famed ‘difficulty’. The corollaries of this deep relationship between w and s stress and the conceptual categories of function and content are highly complex, and crucial to any real understanding of poetic speech. For now, I would ask the reader to take it on trust that the connection between the two is virtually mechanistic: despite them having no immediately apparent connection, a change in state of one will immediately effect a change in the other.
1 Ternary patterning is possibly also present at a dimetronic level in the over-determinations of the literary line we call iambic pentameter. I’ll describe this way of looking at i.p. as a ternary Apollonian sophistication, a kind of Ubermensch waltz, a little later. I think it’s a minor feature of the line, but it may be weakly perceptible at times.