The differences between signifier/signified and reference/sense

The two distinctions:

1. signifier/signified
2. sense/reference (sense/meaning as in the original sinn/bedeutung)

are not only not the same, they are not even particularly related (other than both dealing with meaning). Although, I can see how the confusion could arise.

1. signifier/signified distinguishes between two aspects of a sign - the thing that is used to refer to something and the thing (or rather our mental image of the thing) that is being referred to. Thus "dog" is the signifier and an (our mental image of) an actual dog is the signified.

2. sense/reference help us differentiate a case where 1 signified has more than 1 signifier. Frege gives the famous example of 'The Morning Star' and 'The Evening Star' which both refer to the same object ie Venus (yet another signifier/sense).

This is a different use of the word 'sense' from what you will find in lexicography where 'sense' refers to the different related meanings of a single lexical item.

The reason these two distinctions are not related is because they try to solve different problems. Frege was concerned with solving problems of logical semantics based on the truth conditional theory of meaning. Whereas Saussure (originator of the signifier/signified distinction in its most well-known form) was simply trying to delineate the field of linguistics. In my view, both distinctions are being made more of than they deserve and introduce more issues than they solve.