As the authors point out, language abounds in allusion - the better read you are, the wider your knowledge base, the more you'll recognise and appreciate allusions. But some allusions can become almost commonplace. Suggest that 'Big Brother is watching you', many will appreciate the allusion to Orwell's work, but it doesn't necessarily take an appreciation of '1984' to recognise the significance of the allusion. The authors acknowledge that they tend to confine themselves to allusions drawn from Christian mythology (one of the authors, Abraham H. Lass, has written a book about Biblical allusions), and it's evident they focus on English literature (Shakespeare gets many a mention). Published in 1989, it's a book which may very well be irrelevant now - most people will check meaning online and will have a much wider and more cosmopolitan range of allusions to which to refer. Limited in its scope, perhaps now an anachronism, it remains an interesting wee tome to skim.