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Why should it be that developmental problems with speech and / or language are typically complex’? Dyslexia, and speech and language disorders and disorders with respect to what are known as ‘metalinguistics’ seem to happen together far more frequently than would be expected by chance. It is hard to see how a metalinguistic issue, for instance, could have any plausible connection with a problem sequencing consonants. Why should this be?

If a set of issues commonly occur together, they are known as co-morbidities. A co-morbidity is not a disease, but just the co-occurrence of more than one condition in a significant proportion of individuals.

The co-morbidities include:

  • Disorders involving what are known as ‘speech sounds’ or ‘phonemes’ or delays in their development;
  • Getting the words or phonemes in the wrong order;
  • Difficulty putting words together into sentences with subjects like I in “I fell over”;
  • Problems with reading and writing;
  • Problems with physical co-ordination;
  • Poor ability to discriminate and identify sounds of any sort against a background of noise of some different sort, or to remember a sequence of random items, together often characterised as ‘(Central) Auditory Processing Disorder’.
  • A poor awareness of  metalinguistics.

These co-morbidities are well-agreed and have been extensively studied, but not as a complete set, and not with regard to the theoretical problem which they pose by the sheer fact of their occurrence together

They are sometimes taken to constitute a challenge to the notion of ‘Specific Language Impairment’. If co-morbidities are characteristic, what is the sense in calling the disorder ‘specific’?

The problem of the co-morbidities has three sides: What is the over-arching commonality? How is it that they occur at all? And how is it that there is some order in disorder?

Disorders or delays with phonemes

Difficulties with the ordering and articulation of phonemes are often attributed to the the positioning of the tongue in the mouth and sequencing of the necessary movements and gestures. But it seems to me that at least some of these difficulties, if not most of them, should really be attributed to the way the phonemes are assembled and ordered as components of words in a complex structure.

Missing subjects

Another contribution, in the case of children learning English at least, consists in a difficulty learning that in the overwhelming majority of sentences there is a subject, or a form taking the place of the subject, i.e. it or there, and a verb. If such children are shown a picture of someone eating, and are asked: What is happening? they think that “Eat” or “Eating” is an OK answer. Of course, as an answer that shows that the question has been more or less understood. But it also shows a misunderstanding about what makes English different from languages like Italian, Greek, Spanish, in which the equivalent of “Eating” would be OK. Such children misunderstand how English works at a deep level. This limits their understanding of sentences where there is some reference to something like the ‘subject’. In other words, most sentences. A serious issue for the children affected.

Two sorts of dyslexia? Or more?

In 1878 a German doctor, Adolph Kussmaul, introduced the term ‘word blindness’ to describe a combination of reading problems and saying words in the wrong order which he had seen in several patients. But his name for this gave priority to the problem with reading or what is now known as ‘dyslexia’.

Updating Kussmaul’s observation, it is now clear that there is a constellation of issues which commonly go together.

It is sometimes said that there are two sorts of dyslexia, being unable to see the shapes of the letters, or being unable to hear the sounds apart. Or these skills can be broken down into smaller chunks, making more sorts of dyslexia.

But no matter how many sub-ordinate components there are, this does not resolve the general co-morbidity issue.


Why should these ‘co-morbidities’ exist? Engineers would ask: What is the commonality? The question is sharpest in relation to the co-morbidity between difficulties with respect to speech, where there is clearly and obviously a physical aspect, and a defect with respect to metalinguistics, where there is clearly no physical aspect of any sort. The notion of a physical commonality is plainly absurd.

One possible approach to the commonality issue is by the idea that speech and language have a single architecture and that an underdeveloped sense of metalinguistics is an intrinsic part of the problem for many children who can’t make themselves understood, rather than a separate issue.