The major thesis of this theory was that the word meaning is the actual referent. The meaning of a tree is the actual referent that occurs or the object in the world. This approach encounters some serious difficulties. What about those words that lack reference such as: a dragon, a unicorn, Pegasus, etc. Philosophy would say that we cannot observe unicorns but we can have a mental picture about them. Extension is a part of meaning that includes all the possible occurrences of the referent. Intention is the sense part of the word and it evokes different associations. Since reference is not enough, what is the sense of the words? Semanticists say that the word meaning should correspond to some mental images, word meaning is the image of the referent. This is the Image Theory of Meaning. There are some words such as: hello, but or and that cannot create an image and also have different images about things, e.g. dog - it is difficult for all the speakers to have one general image of a dog. That is why the approach of direct linking between the word and the referent is abandoned. The word meaning should be presented by a mediator medium, which means mentally represented reference in our mind.