Although it is argued that root and epistemic meanings are rather different in nature, from studies discussed below (Sweetser 1990, Pelyvás 2000) we can clearly see that this does not mean their absolute difference. They are indeed related, or can be explained as related domains. The means by which they are brought into contact is called metaphorical extension. We apply the same modal verbs to the epistemic and real world because we find the force-dynamic structure of the epistemic world and the sociophysical world parallel. Other elements of the English lexicon may well be expected to represent a similar ambiguity between real-world and epistemic force. Modality is one particular vocabulary domain which shows synchronic ambiguity between the external and internal worlds (Sweetser 1990:49) hence I will talk about this topic in more detail below. (Introduction)