| This article is part of the grammar course.
You may choose to follow it in a structured way, or read each item separately.
The most central unit of grammar is the clause. This is hard to define, but it is essentially a group of words that contains a verb and expresses an idea, more or less completely. Clauses make up sentences; sentences can contain one clause (a simple sentence) or several.
Any of the semantic words in a sentence can be replaced by a clause or a phrase. Indeed, grammar has words to name this phenomenon. An adjectival is a word used to name a unit - of any size (word, phrase or Clause) -- that does the work of an adjective. Similarly, an adverbial is any unit that fulfils the function of an adverb, and a nominal is a unit that acts as a noun. (In addition to these noun uses, adverbials and the others may be used as adjectives. We can have an adverbial Clause, for example, as well as an adverbial; and we can have an adjectival phrase and a nominal Clause.)
(As a verb is the essential ingredient of a clause, there can be no such thing as a '
verbial'. However, verbs in English very commonly contain more than one word, so the verb phrase is very common. This is the phenomenon where a single meaning is conveyed with more than one word, e.g. "He may have been being cheated".)
The next section of the course expands on the structure of a clause.
A particular type of clause is the relative clause, which poses some problems in punctuation.