According to their derivational pattern, English interjections are as a rule divided into primary (simple) and secondary (derivative). Primary interjections (ah, hush, oh, ouch, ugh, wow) stem from reflex involuntary exclamations and sounds that represent the speaker’s immediate reaction to a certain event. Contrary to reflex exclamations and sounds that do not belong to the language, interjections are linguistic signs, conventional in a certain language community, intelligible for its members, since these signs convey a certain meaning.

Secondary interjections are derived from lexical words (or word forms), e.g. blimey, boy, Christ, chrissakes, dear, gees, Goodness, my, why. These lexical words, having sometimes undergone phonetic transformations, turned gradually into a means of expressing human emotional impulses. Since the source-words still function in the language and parallel the derivative interjections, the main identification criterion to distinguish between them is the unity of their semantic and grammatical properties.

It has already been mentioned that interjections differ from other parts of speech in that they express nomination in a peculiar way. This property plays a crucial part in differentiating between interjections and their homo­nyms and between emotive lexical words. For example, the adjectives super, gorgeous, awesome, uttered with a certain intonation, though expressing the speaker’s attitude to some event, still may not be qualified as interjections, since they express a qualitative evaluation of some phenomena and, conse­quently, have a definite logical lexical meaning. The homonym of the noun, the interjection Goodness that expresses the speaker’s emotional reaction does not name any phenomena and does not characterize them in any quali­tative aspect: the interjection only indicates the type of the emotion.

Semantically, interjections are as a rule divided into two groups: those expressing emotions (emotional interjections) and those expressing in­ducement (imperative interjections). Research proves that the first group is formed by an overwhelming number of items, whereas the second is less numerous (come on!, here, hey, hush, lo, etc.).

Imperative interjections differ from emotional ones in that their meaning is, as a rule, more transparent and independent of a context and a situation. But it would be wrong to treat this difference as absolute, since there is a number of emotional interjections with a quite established meaning, e.g. alas, bravo, hurray, ouch, wow, etc. These interjections are referred to as “meaningful”. They should be distinguished from situational ones, i.e. those expressing emotions in general: cf. ah, oh, God, Goodness, phew, etc. Obviously, the term “meaningful” may also be used to describe imperative interjections, but they are clearly different in that they express inducement or volition.

Structurally, English interjections may be divided into two types: simple and composite. Simple interjections have the structure of a separate word. Composite interjections are forms combining several words. Interestingly, primary interjections are almost always simple. Composite interjections are relatively rare. They are mostly formed by combining two or more simple interjections, e.g. dear me, confound it, hang it, etc. Sometimes linguists claim that the number of secondary interjections is overextended. The lin­guists doubt whether units of various language levels (such word combina­tions and sentences as Good Gracious, I am hanged, Well, I never, etc.) may be classed as interjections. The scholars argue that though these items have acquired the features of set expressions, still their transition into a part of speech has not been completed. The proponents of this point of view claim that the majority of these word combinations and sentences still preserve internal syntactic relations between their components, that they are inter­nally divisible and may rather often change their components. Syntactically, though, they are homogeneous units, when used as emotive sentences.

The described controversy makes it possible to conjecture that develop­ment of interjections out of word combinations and sentences starts with their gradual idiomatization that results in various word-building and pho­netic shifts within these word combinations (cf. attaboy (that is the boy), blimey (blind me), dammit (damn it), durr (dear me), for chrissakes (for Christ sake), omigosh (oh my God), etc.).

The opposite point of view is based on the argument that word combina­tions and sentences may be given the status of interjections on the ground of their semantic, syntactic and morphological properties. The supporters of this approach suggest that it suffice to indicate the complex structure of these interjections in the term “interjection phrase”.