To be completely honest, this was a tough read for me. I felt lost while reading, and the concepts were pretty hard to grasp. But what I interpret as the difference between linguistics and semiology is that semiology is the reflection of the rules placed on different symbols, signs and words etc used in language. It governs how the words are used and their meanings. Linguistics on the other hand studies the auditory and physiology of communication between two or more people.
In addition, the author is also making the claim that linguistics is only a branch of semiology. That the system of signs is the whole in which language derives from. “A science that studies the life of signs within society.” This implies that semiology stems from society and how society perceives and uses these signs. Semiology can be used to put a value on the sociological impact of different symbols.
Studying different cultures and practices associated with them can shed more light on language. Studying linguistics on it’s own and following it’s set of rules only serve to separate it from semiology and all other things associated within society. Looking at it from the viewpoint of the individual it ignores the sociological structures. But looking at it from a social standpoint it would take the value away of the individual.