"The test for allusion is that it is a phenomenum that some reader or readers may fail to observe" [12, p.39]Allusions are far from being the sole preserve of literature. Cinema, painting and music frequently contain quotations from other works. Early still-lifes in particular depended on a rich vocabulary of symbols which many admirers are unaware of today. But how important for the contemporary reader is the awareness of a poem's allusions? And how has this importance changed?
recognition of marker - If an allusion is disguised or unobtrusive (it doesn't appear in quotes, it has a tempting non-allusive interpretation, etc) the reader may not realise that it exists. Some poets may use this ploy to satisfy certain readers for whom "the pleasure of recognition [is] proportional ... to the difficulty or unobtrusiveness of the allusion". I.A. Richards said that these ploys are "not to be confused with literary or poetic values" [13, p. 170] but it's at least "tactful" (as Empson called it [7, p.167]) of the poet to give the words that form the allusion a meaning in their own right. This, however, increases the risk of the allusion being missed and if the intrinsic meaning is plausible but weak, the reader may miss much. The poet may intend the reader only to recognise the allusion later, or for only a part of the readership to pick up the allusion - examples are dramatic irony, in-jokes, pantomime asides and innuendo. Plagiarists hope that the marker won't be recognised at all.
Some poems can survive the loss of this allusive power - indeed the reader's attention may be profitably focussed back into the text (for instance, some parodies work even if readers are unaware of the original. Yet there's a certain effect produced by references out of the text, whether they're spoofs or not; they show ways out of the poem, and often ways back in.
identification of evoked text - There is no longer a canon of work that the reader can be expected to know - readership is wider, the Bible is less popular, and there are more books. Modernist authors are more likely to allude to obscure, private, ephemeral or even non-existent texts. When a text refers to many, widely ranging texts, noting one allusion is less likely to prime the reader for the next. To circumvent this, some poems explain even well-known allusions within their text or by footnotes.
modification of the initial local interpretation of the passage - Pre-modernist poems more often than not had a primary meaning, perhaps based on initial observation. Once established, this meaning could pull in an allusion without being overbalanced; the poem's centre of gravity remained within the text. Nowadays, poems need no longer establish a solid melody before improvising. Some set a foundation by alluding to the canon or genre, others don't even try. There has been a re-ordering of linguistic priorities: common, denotative meanings becoming secondary. Where there is no primary meaning, significance is distributed. The poem loses its surface, its graduations of depth. The allusions more prop up than dangle from the poem. Attention is diffused.
activation of evoked text - "While reading text, readers establish local coherence in short-term memory - small scale inferences from few small units of information... These hypotheses are refined as the reading of the text proceeds ... In semantic memory, each concept is connected to a number of other concepts. Activating one concept activates its adjacent concepts which in turn activate their adjacent concepts. Thus, activation spreads through the memory structure, determining what is to be added and what is to be removed from the interpretation of text. This process continues until further activation of adjacent propositions does not change the propositions used to interpret the text." (quoted from  which in turn acknowledges ). Activitation spreads more easily through and beyond the remote text if there are repeated references to the same text (parody) or if the remote text is far more interesting than the base text, especially if the base text lacks coherence.
Wallace Stevens, in the context of metaphors, said "The proliferation of resemblances extends an object. The point at which this process begins, or rather at which this growth begins, is the point at which ambiguity has been reached" . If what's evoked merges into the presented text, the text becomes "an entrance into a network with a thousand entrances" [4, p.12], and we are as likely to take a further leap away than return to our point of departure. Alternatively, the text alluded to may not so much extend the original text as help create a new third entity. As in "Surrealist metaphor, two terms are juxtaposed so as to create a third which is more strangely potent than the sum of the parts...The third term forces an equality of attention onto the originating terms" [16, p.73-74]. When ordinarily unassociated elements are juxtaposed, the reader is called upon to determine. But if this determination is not logically possible, if the relation between the two is undecidable, something else appears in this gap. Eliot and Pound even spoke of "emotion" in this context.
Computer modules also differ in the extent that they interact with each other. Programmers aim to write modules that have strong cohesion and weak inter-module coupling. Extending these concepts leads to a way of classifying poems. The traditional sonnet tends have strong cohesion (emphasised by the form) and is weakly coupled to other poems, whereas a typical modernist piece (The Waste Land) has weak cohesion and strong coupling/inter-textuality. The cohesion of computer modules isn't easily measured or characterised, but one can make a rough assessment of a poem's cohesion and coupling by comparing the number of internal and external references. If a poem's cohesion is strong then it can survive allusions being missed (and indeed, they're more likely to be missed).
A CARAFE, THAT IS A BLIND GLASS - Gertrude Stein
A kind in glass and a cousin, a spectacle and nothing strange a single hurt color and an arrangement in a system to pointing. All this and not ordinary, not unordered in not resembling. The difference is spreading
The weak semantic and formal cohesion are hallmarks of a modernist text. The weak coupling in this example puts a further strain on the reader.
Her smile - Tim Love
Her smile as she falls asleep -
a bird always
landing on its shadow.
Weak coupling (drawing on the genre but not on any particular text) and strong semantic cohesion typifies the lyric poem.
Animal Lover - Tim Love
Dolphins always smile my way on salmon-
Chanted evenings and hawkmoths wink all night.
O stuffed dodo do what you done done done
Before, you toucan with your songs delight.
Yes, I confess my sole intent; to wit
To woo beasts two by two, pander and bare,
Cheer the worm's turn, watch horses get a bit
On the side, then, with swallowed pride, home where
My faithful quick brown fox jumps just for me.
How long can this go on? Is my fate sealed?
Oh deer, paw me. But if I must I'll flea -
I'll go to the dogs or pick up booze-swilled
Slugs then flock to packed terraces and crow
"O earwig, O earwig, O earwig O!"
The form and thematic continuity do little to disguise the lack of higher level cohesion. The extensive use of puns to convey references means that coupling isn't wholly at the expense of the primary text. The references lead nowhere and don't interlink; if a few are missed it's not the end of the world. They're one-way - the poem doesn't suck significance in from distant texts. The combination of weak cohesion and numerically strong coupling is common in ludic and post-modernist work.
Paradox - Tim Love
You haven't left her, only she moves,
and when she has stopped moving
it's as if you left each other
and it all makes sense on paper
until the platform moves,
and you are not moving.
Those who know about relativity (the Twin Paradox in particular) have a distinct advantage when reading this piece because attention isn't drawn to the allusions. The semantic cohesion and a measure of pattern give others some chance of satisfaction, enough to make them think that they haven't `missed something'.