Lexicology

Lexicology is basically understood as the study of lexis (vocabulary or stock of words of a language). Stock evokes the idea of a set of words which brings the idea of the lexicon. The vocabulary is understood as meaningful units
Lexicology is closely linked to morphology. In lexicology what matters is the meaningful side of the words. And in morphology what matters is the form of these units. The form and the meaning of a word may be related so they are closely linked. Meaning takes us to semantics. Part of the semantic studies is based in meaning: lexical semantics. So lexicology has links to many other areas, but our vision of lexicology is restricted. Etymology is a branch of linguistics on its own. It's regarded with words and its history.
We should never mix lexicography with lexicology because it's not a branch of linguistics but a technique and has a very narrow aim. Lexicography deals with the making of dictionaries. So it's not a level of languages. We have a narrow concept of lexicology: it's a branch of linguistics concerned with the meaning and use of words. There is a diversity of approaches which goes from narrow conceptions to very wide conceptions.
In sentence semantics we can predict the meaning of the whole sentence because we have rules that show it to us. The limit is in lexical semantics, because here we don't have any possible combination that allows us to guess the meaning of a word. So “in linguistics is simply axiomatic that words have meanings.

·         SENSE AND REFERENCE

When we deal with the sense we deal with relationships within language. When we talk about reference we deal with the relationship between language and the world. By means of reference a speaker is pointing at something in the world by using language / a linguistic expression. Therefore with reference there is always an external reality that is being talked about.
It would wrong to think that every linguistic sign corresponds to some external reality. One single linguistic expression may point to different entities of the outside world.
Ex: Your left hand
There are different entities in the outside world that refer to this same expression.

This is called variable reference. The perception of variable reference depends on a number of factors, which are there because of the relationship between language and the world. There are factors like time and place that play and important role in this.
Ex: The British Prime Minister
Does this expression have a referent? Yes. You could say Tony Blair but you could also say Margaret Thatcher. In this expression the time factor isn't expressed so both possibilities are possible. The question of place is specified so you can't say Aznar because it has to be British. If you say the current British Prime Minister, there is no variable reference.
In this relationship between languages and the world we also have expressions which only refer to one entity in the outside world:
Ex: The moon, the sun…
They are not so frequent and they don't raise any semantic problems at all and they are not interesting for the purposes of lexical semantics. We can also find a number of linguistic expressions referring to one referent in the outside world:

Ex: The Morning Star
Venus
The Evening Star
In English, there are two expressions that refer to the same entity. This example is always like that, but there are cases in which this association between single entities in the world and different linguistic expressions can be also be made for specific cases.
The British Prime Minister
Tony Blair
The Leader of the Labour Party
This relationship isn't permanent. It has been made for a specific purpose.
That these expressions may be true depends on time and time factors.
Ex: John
The man at the corner
In a specific case these two expressions may have the same referent in the world.
Whenever you talk about reference there is always something in the outside world pointed out by an expression. When we talk about sense what we find is that the sense of a word is its place in a net of semantic relationships within a language. Sense is a purely inherently linguistic phenomenon. Sense is very difficult to define, but very easily perceived by native speakers. The clearest for a native speaker is `sameness of sense'.
Ex:
Almost has the same sense as nearly. These two words occupy the same place in the net of relationships in a language. The same happens with vertical and upright.
John took off his jacket
John took his jacket off
They have different syntactic structures but they have the same sense.
Bachelors prefer red haired girls.
Girls with red hair are preferred by unmarried men.
They also have the same sense.
The opposite also happens, that is, we may have two different senses and one linguistic expression. This is the case of polysemous words.
Ex:
Bank (of money)
Bank
Bank (of a river)
One single sentence can also have more than one sense. These sentences are represented in two different trees depending on the sense.
Ex:
The chicken is a living animal and is going to eat.
The chicken is ready to eat.
The chicken has become a meal and is ready for us to be eaten.
It's a lexical question.
If `with a smile' is a constituent of the higher level, the one who smiles is `He'
He greeted the girl with a smile.
If `with a smile' is a constituent of the lower level, the one who smiles is `the girl'
It's a syntactic question.
Sense is an abstraction, therefore, if you say a linguistic expression has a meaning, it's because it has sense but it may not necessarily have reference because not all words connect with an entity in the outside world. And this is a rule.
Ex:
So, in, at, over, either, onwards, and, almost: these words have no reference in the outside world.
Mind / Thought
Language World