I have used the term ‘core of a word’ in a rather vague way, to denote the morpheme that makes the most precise and concrete contribution to the word’s meaning. I have also refrained so far from using two terms that may be already familiar to you: prefix and suffix. It is time now to bring those two terms into the discussion, and also introduce the term root for what I have been calling the ‘core’.

It emerged that, in the native Germanic portion of the vocabulary, the root of a complex word is usually free. Of the non-root morphemes in the words that we have looked at so far, those that precede the root (like en- in enlarge) are called prefixes, while those that follow it are called suffixes (like -ance in performance, -ness in whiteness, and -able in readable). We have encountered far more suffixes than prefixes, and that is not an accident: there are indeed more suffixes than prefixes in English. An umbrella term for prefixes and suffixes (broadly speaking, for all morphemes that are not roots) is affix.

Only root morphemes can be free, so affixes are necessarily bound. We have already noticed that the morphemes -ful and -ness of helpfulness cannot stand on their own. It is easy for anyone who is a native speaker of English to check that the same is true of all the morphemes that I have identified as prefixes and suffixes in (1a) – that is, all the morphemes in these words other than the roots.

At this point, it may seem to some readers that terminology is proliferating unnecessarily. If affixes are always bound, do not ‘bound morpheme’ and ‘affix’ mean essentially the same thing? Likewise, if roots are usually free, do we really need both the terms ‘root’ and ‘free morpheme’? The answer lies in the word ‘usually’ in the previous sentence. Affixes are indeed always bound, but it is not the case that roots are always free. In fact, all the words in (1b) have roots that are bound. The fact of being bound may make a bound root harder to identify and isolate as a morpheme than a free root is; but for most of the examples in (1b) it is possible to find other words in which the same roots appear, such as audible, auditory and audition alongside audience. A cranberry morpheme can be thought of as a bound root that occurs in only one word.

We have so far encountered two main kinds of complex word: ones with a single free root, as in (1a), and ones with a single bound root, as in (1b). Is it the case, then, that a word can contain no more than one root? Certainly not – indeed, such words are very common; they are compounds, already mentioned in connection with cranberry morphemes. Examples are bookcase, motorbike, penknife, truck-driver. The point of mentioning compounds again now is that, if a complex word can be formed out of two (or more) free roots, it is natural to ask whether a word can contain two or more bound roots. The answer is yes – although, in the light of the English language’s preference for free roots, they are not nearly so common as ordinary compounds. Examples of words with two bound roots are electrolysis, electroscopy, microscopy, microcosm, pachyderm, echinoderm. Other words which, like cranberry, contain one bound and one free root are microfilm, electrometer and Sino-Japanese (assuming that Japanese contains the free root Japan). It will be evident straight away that these are mostly not words in common use; in fact, I would expect few readers to be familiar with all of them. Unlike ordinary compounds, these words are nearly all technical terms of scientific vocabulary, coined self-consciously out of non-English elements, mostly from Latin and Greek. Because of the big difference between ordinary compounds and these learned words, and because of the non-English character of the bound morphemes that compose them, many linguists and dictionary-makers classify these bound morphemes as neither affixes nor bound roots (such as we encountered in (1b)) but place them in a special category of combining forms.

Given that native English words generally contain free roots, we might expect that, if a word made up of combining forms is in common use, the morphemes within it should tend to acquire the status of free morphemes. This expectation turns out to be correct. For example, the word photograph existed, as a learned technical term composed of combining forms, before the word photo; but photo must now be classified as a free morpheme. Other combining forms that have more recently ‘acquired their freedom’ are micro- and macro- (as in at a micro level or on a macro scale) and retro-, as applied to music or fashion.