Within the great collection of things that have been labeled "particles", we find at least one grammatically significant class of items, in English and in languages generally. These have been variously termed "discourse particles" and "interjections"; here I will call them "discourse markers". On the ground of distribution, prosody, and meaning, discourse markers can be seen to form a class. [...] they are independent words rather than clitics [...]. On distributional grounds, the traditional class of exclamatory "interjections" in English-items like "ouch,boy, gosh, holy, cow, now, my goodness, dear me" and "hell" - should also be grouped with these markers.
- Zwicky (2004), a pag.372