Visible speech is another way of refering to writing with phonograms or sound signs. This was the name that Melville Bell gave to his iconic notation.  Bell's goal was to devise a system of marks on the page that had some kind of direct relationship to the sounds produced by the exercise of the organs of speech.  The visible speech notation indicated what articulators were involved in producing each speech sound.  The b sound /buh/ was represented as
 

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Bell's system was fine for phonetics, but was more complex than it needed to be for phonemics or the representation of the meaningful sound categories of speaking and listening.  It was a system for phoneticians not one for everyday communication.

Communication is dependent on dividing up the continuous sprectrum of speech sounds into discrete categories of meaning called phonemes.   phonology-course.html 

The speech organs are capable of producing about a million different acoustic variations, only about forty of them are required for communication.  Learning to communicate involves training the ear to ignore most of the variations and treating a range of different sounds as if they were the same.  foneemz44.htm  fon-inventori.html 

There is an acoustic difference between the T in [tin] and [nit]  but this can be ignored in English because it does not discriminate a difference in meaning.  Acoustic or phonetic differences that don't make a difference do not need to be isolated in a notation.

If there are only 40 sound categories, then no more than 40 marks are needed to represent them.  The 40 sounds is somewhat of an oversimplification since consonants cannot be articulated without adding a vowel.  Alphabets may be somewhat more abstract than syllabaries and somewhat more difficult to teach and learn. Speech patterns in an alphabetic system are combinations of V's [vowels] and C'sn[consonants].  CV VC CVC.  In his book, Story listed all of the combinations that were used in English. 

On the other hand, some of the sound categories included in the 40 basic sounds are blends or glides, not new vowels or consonants.  There are 12 uncombined vowels and 22 uncombined consonants plus schwa.  Schwa is a shorter unstressed version of a mid-central vowel found in [her bird word curd].  Isolating the schwa distinguished the vowel in her /h':r/ from a similar sound found twice in another /'nLd'r/.   The three r sounds [rC] [ 'r]  and [Cr] can be found in the [roar] [rower] distinction.  /rour/ / rou'r/.  The difference between Cr and Cr is not phonemic.  In some dialects [rCr and rC'r] cannot be distinguished.

This brings the total number of uncombined sounds to 35.  Five frequently used combinations [c for tsh, ai, ei, au, oi, ou] are traditionally added -  bringing the total to 40.  If  [hw and yu] are  added, the total  climbs to 42.  The following table isolates 50 sound categories.

 4x6-table.html  ccs2charts.html 
  

Traditional English uses 106 digraphs to represent 40 sounds.  About 70 are important enough to isolate and teach.  Some of these digraphs are used to represent more than one sound.  There are code overlaps.  [e.g.,  ey ay]  as in [they key eye] and [kay aye].  [for more code overlaps, see the poems] [writing samples, writing samples 2]
 
 

Bell's system worked but did not catch on because it was difficult to draw and had no relationship to Roman letters.
 

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