The semantic theory of language is based on some basic pre-suppositions.

The most fundamental one is that each element of communication can be divided into two sides: the signifier and that which is signified.

• On the signifier side, is the "material" element, that which can be physically seen or heard, the element which is possible to transmit physically from one end to the other: this element is called the code, the conveyor, the symbol, etc.
• On the side of the signified, is the "spiritual" factor of communication, that psychic element which is represented by the symbols and which is called the message, the meaning.

Alternatively, these are called the form and the substance; the style and the content, etc. But whatever be the denomination, the semantic approach is based on a dichotomy which considers what is being transmitted as separate from the process of transmitting it.

This dichotomy is a consequence of a more basic distinction between a transmitter and a receiver of communication. The classical model of this approach is the famous linear model:

S --- E --- D --- R

Where S is the sender, E is the process of encoding, D is the process of decoding and R is the receiver.

The sender has in his mind a mental image, a meaning, that he intends to communicate; but he cannot convey that meaning unless he transforms it into symbols. So symbols are coded and then transmitted through the channel; on the other end, there is the receiver, who decodes the message, and understands the significance of the symbols, i.e. re-constructs the original mental image.

The difficulty of this theory concerns the process of cementing the mental with the material. The elements which can be transmitted are "the symbol"; but the symbol by itself doesn’t have a meaning, and acquires the meaning by the process of communication itself. So while the semantic theory is very elaborate in differentiating various elements, phases, links, rules, etc. of the communication process, it does not try to explain how the meaning, which is a "mental entity" gets cemented to the symbol, which is a "physical entity".

A direct consequence of this dichotomy is the idea that the sentence is understood because the symbols are understood. So, at the beginning of the communication process, the sentence is de-composed into symbols; these symbols are received, de-coded and understood; and because symbols are understood, the whole sentence is understood.

Also, the process of tying the various symbols together in a coherent whole is conceived in material terms. The semantic theory postulates the existence of a "structure" which forms the skeleton upon which the sentence is composed. This structure is made up of semantic rules and linguistic patterns. By understanding the structure, the sentence is understood: when one knows the structures of the language, one understands what the language expresses.