A correspondent asks whether hyphenated or non-hyphenated forms are the norm in such linguistic terms as phrase marker, form class, word class, and so on. How to find out which is the norm?
There is no absolute rule. Some publishing-house style-guides recommend hyphens and some don't. This isn't just a matter of technical terminology, of course. We find both flower pot and flower-pot (and flowerpot). Generally, the tendency over time is for English compound words to begin spaced, then to be hyphenated, and then maybe to be written solid (no space or hyphen). The more familiar the term becomes, the more likely it is to be perceived as a unit, and hyphenated. So we are much more likely to see terms hyphenated which have been around a long time, such as word-class and phrase-marker. But a lot depends on the extent to which the expression is perceived to be a semantic unity, as opposed to two separate notions. Word root, for example, is less likely to be hyphenated.
Usage is strongly influenced by legibility. There is a big difference between these two cases: 'X is a word class' and 'X is a word class analysis'. In the second case, there is uncertainty as to whether the writer means 'word-class analysis' or 'word class-analysis' , so a hyphen resolves the matter. Look at the sentence I used above: if I had written ' Some publishing house style guides', it would have been much more difficult to read. So one factor is whether the compound is being used attributively (before a noun) or not. Many style guides insist on a hyphen in attributive position.
How to find out which is the norm? The best way is to look in an up-to-date (that's important) dictionary. Alternatively, an online check in a search-engine will give you a quick impression about frequency.