Submodalities are subsets of the modality of which we internally represent something. They are how we code, give meaning and order thinks in our mind.
For example, if you think of being loved - you will represent that as either one or all modalities of a picture, sound, smell, taste or feeling.
Submodalities are subsets of each of those modalities.
If you seen a picture, the submodalities may be that the picture is in colour, it is located near your face, you can see yourself in the picture, its big in size etc. They allow an NLP Practitioner to get the information needed to make a change of an internal representation without the content.
One of the benefits of NLP is that most of the work is content free. It allows us to work with a client quickly without delving deep into the story.
By changing the internal representations, you can make significant change quickly and without associating the client into the negative content of a story.
I use this for clients who want to stop eating things like chocolate, chips, sweets, deserts, soft drinks and many other minor states and behaviours.