English Grammar Analysis: tree diagrams

The constituent that we will see most is the phrase. A phrase consists of a single main word, called the head of the phrase, and other words that modify or give grammatical information about the head. These other words in the phrase are called the phrase's attributes. Informally, we might say that the head word is the main idea of the phrase.

(2) Russia's proposal at the conference

The phrase in example (2) is talking about a kind of proposal. Russia's and at the conference tell us what specific proposal we're talking about. Proposal, therefore is the head word.[1]

The lexical category of the phrase's head gives its name to phrase. Thus a noun is the head of a noun phrase (abbreviated NP), a verb the head of a verb phrase (VP), and so forth. Since proposal is a noun, (2) is a noun phrase.

Other Examples:

(3a)	baked him a cake	Verb Phrase (VP)
(3b)	fond of pecans	Adjective Phrase (AP)
(3c)	very quickly	Adverb Phrase (AdvP)
(3d)	to the lighthouse	Prepositional Phrase (PP)

Apart from simply being a convenient way to name phrases, the relationship between the head word and the phrase type captures a significant fact of syntax: the category of the head word plays an important role in determining where in the sentence the phrase can go, as well as a variety of grammatical rules such as agreement between subject and verb.

(4) {The [contract] between the boards of the two companies} [was] nullified by regulators.

For example, in sentence (4), contract is the head word of the NP which is the subject. The whole subject, therefore is singular, and agrees with the verb was, despite the two plural nouns (boards and companies) which are closer to the verb in terms of linear order, but which are actually buried in prepositional phrases.[2]

This example also illustrates another important point: phrase structure is hierarchical. That is, phrases can nest within phrases to any level of complexity. Thus the subject of (4), "the agreement between the boards of the two companies," contains two prepositional phrases, each of which itself contains a noun phrase. We can show this relationship in a diagram:

Clauses

A clause is a constituent consisting of two parts: a subject and a predicate. The concepts of subject and predicate are probably already familiar to you from your earlier schooling. In terms of meaning, we can say that the subject is the part of the clause about which something is asserted, and the predicate makes that assertion. These definitions are vague, and eventually we will need to be more precise. We will describe a clause in terms of structure once we're better able to describe how that structure works.
(11) 
Subject and predicate are both grammatical functions. The predicate is realized by a verb phrase, and in the most common case, the subject is realized by a noun phrase. Notice that in the diagram above, we indicate both the grammatical form (the phrase type) and the function. The two are separated by a colon. Thus our notation follows the pattern form: function.[1]
One important point to note about subjects is that they frequently consist of more than one word.
(12) 
Many students are taught in grade school to identify the word senator alone as the subject. However, notice that senator is merely the head noun of the subject. The determiner the and the prepositional phrase from California are also part of the subject. In other words, subjects and predicates, along with other grammatical functions we will encounter later, are functions of phrases, not of individual words. As we noted above, however, those phrases may consist of only one word from time to time.

Different textbooks present different variations on the tree diagram, depending on the details of their analysis. The basic principles, however, remain constant, and if you understand them, you should be able to grasp the diagrams' essence no matter what the details. Tree diagrams are most often drawn above the item being diagrammed. A tree consists of nodes. A node has a label, for example NP for noun phrase, VP for verb phrase, and so on. The node at the very top of the tree, the one from which all the others ultimately derive, is called the root of the tree. The nodes are connected by lines, known asedges. The terminal nodes of our diagrams, the ones without any children, are known as the leaves of the tree. They will contain labels for the word categories (parts of speech) of each word. (The following examples contain details that we haven't introduced yet. Don't worry about these yet. It's only important here that you understand the general message that the diagram is meant to communicate.)Borrowing terminology from genealogical trees, the nodes below another node are sometimes called the children of that node. A node that has children is a parent node. Just as with people, parent nodes can themselves be children of other parents. If we need to talk about nodes that are children of children, we call them descendants. Unlike genealogical trees, however, it is important to note that while a node may have several children, it only has one parent. Also, each line should connect to one child node. Do not show two edges connecting to a single word.

Further, you should always space out your nodes so that edges do not cross one another. This practice is merely for visual clarity. In principle, there's no reason why the lines must never cross.

Sometimes, we will not want to analyze a sentence completely. Initially, we will lack the knowledge to analyze everything in a sentence. Later on, with more complex sentences, we may choose to ignore details that aren't relevant to our purpose. In these cases, we will indicate an unanalyzed constituent by using a triangle.