Difficulties have been recognized in adequately defining synesthesia: many different phenomena have been included in the term synesthesia, and in many cases the terminology seems to be inaccurate. A more accurate term may be ideasthesia.
In one common form of synesthesia, known as grapheme → color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored. In spatial-sequence, or number form synesthesia, numbers, months of the year, and/or days of the week elicit