Every now and then a reader will ask me why I don’t use Reed-Kellogg sentence diagrams, or what I think of them, or recommend them over the tree diagrams I use. So I’ve decided it’s time to begin a series of posts comparing the two ways of diagramming sentences — or in the case of tree diagrams, phrases. They’re not limited to just sentences, which is one reason I prefer them.
The most recent person to write to me about R-K diagrams is Martha Kolln, a retired English professor at Penn State, and author of several grammar books. She argued that R-K diagrams “clearly [show] the differences among transitive, intransitive, and linking verbs.” This seems like as good and limited a topic as any to start with, so here goes. I’ll start with intransitive verbs, with the sentence Syntax rocks. The R-K diagram of this sentence, shown to the right, has the subject to the left of the vertical line that crosses the main horizontal line. The verb rocks is to the right. That’s all there is to it, because rocks is intransitive, and doesn’t require any direct objects, predicate nominals, or any other kind of complement to complete the verb phrase.
Now let’s see how this looks using a tree diagram. Since the whole thing is a sentence, the root node of the (upside-down) tree is labeled S. To show that this S consists of a noun phrase (NP) subject and a verb phrase (VP), this S node divides into two branches. On the left is the NP node. This NP consists of just the noun syntax, so it has only one branch coming off of it, leading to the N node. The “leaf” of this branch is the noun syntax. The VP node also consists of just one word, the verb rocks. So a single branch comes off the VP node, and ends in a V node, just above the rocks leaf.
So far, the two systems are pretty similar, although the tree diagram explicitly gives information that the R-K diagram assumes you will have; i.e., the category and part-of-speech labels. This will be useful for when we diagram isolated phrases that aren’t part of a sentence.
Next up, a transitive verb, illustrated in the sentence Syntax excites me. As before, the subject is to the left of the vertical line that crosses the horizontal, and the predicate is to the right. This time the predicate consists of the verb excites, and its direct object, me. The direct object appears to the right of another vertical bar, which does not cross the main horizontal. This is the hallmark of complements of verbs other than linking verbs in the R-K system.
Now for Syntax excites me in a tree diagram. The NP subject is as before. This time, the VP node branches into the V node for excites, and another NP node for its direct object. Thus, both systems distinguish between intransitive and transitive verbs. The direct object NP consists of the pronoun me, so just a single branch ends in a Pronoun node followed by the leaf me.
Finally, let’s look at linking verbs, with the sentence Syntax is awesome, which contains the linking verb is and the predicate adjective awesome. The R-K diagram on the right is like the other two as far as separating the subject syntax from the predicate. R-K diagrams distinguish linking verbs from transitive verbs by having a slanted line instead of a straight line between the linking verb and its complement. The slanting line is supposed to indicate that the subject has the property named by the predicate adjective (or that the subject and predicate nominative refer to the same thing).
Represented as a tree diagram, Syntax is awesome has precisely the same branch structure as Syntax excites me. The differences are that the leaf labels excites and me are now is and awesome, respectively; and that the NP and Pronoun nodes under the VP node are now Adj(ective)P(hrase) and Adj, respectively. The identicalness of these trees means that this kind of diagram does not distinguish between transitive verbs and linking verbs: Both direct objects and predicate adjectives (and predicate nominals and predicative prepositional phrases) are represented as complements of a V — that is, as a sister node to a V under a VP mother node.
How can a tree diagram represent the information of the slanting line in a R-K diagram? From a syntactician’s point of view, that’s not the diagram’s job. That information isn’t about syntax, but semantics. For that matter, neither R-K diagrams nor tree diagrams show that (at least in more formal varieties of English) pronominal complements of transitive verbs are in accusative case (e.g., They criticized her), while pronominal complements of linking verbs are in nominative case (e.g. It was she). To do that, you need enriched diagrams that can show features like these, but that’s a whole nother story.
As a final note, I should note that both kinds of diagram will let you parse an ungrammatical sentence. You could easily diagram *Syntax excites awesome in either system. To rule it out, you need a set of rules for what kinds of diagrams you can make. In R-K, you need to have a rule that only linking verbs get to have the slanting line after them, and can be followed by an AdjP, and indeed, such rules are taught in the grammar books. For tree diagrams, you need something similar. But with tree diagrams, you have the option of putting some of that enrichment I mentioned above in the category labels, so that you can verify each branching is legit. Below I’ve re-presented all three sentences in this kind of diagram. Here, the labels S and NP stay the same, and Pronoun is simply NP (because pronouns act as NPs). VP has been replaced by NP\S; that is, a VP is something that looks to its left for an NP, and results in an S. Instead of a simple V category for any kind of verb, we have labels showing what kind of complement the verb has to take before it can form an NP\S. Intransitive verbs are NP\S already! Transitive verbs are (NP\S)/NP; that is, they look for an NP on the right before they become an NP\S looking for a subject. Linking verbs are (NP\S)/Pr, with Pr standing for Predicative. This category covers predicative NPs, AdjPs and P(repositional)Ps. The adjective awesome is given the category Pr, since it can act as a predicative adjective phrase. (A noun such as former, though, which can’t be predicative, wouldn’t have this category. Instead, it would be N/N: something that looks for a noun on its right, and results in a bigger noun.) Syntax, by the way, is an NP only because it’s a mass noun, which can act as an NP. A count noun such as sentence would have category N, and would have to combine with something with category NP/N, such as the, in order to form an NP.
The nice thing about this kind of presentation is that at each branching node, you can see the label in the denominator of one daughter node get “canceled out” by the label of its sister node. For example, at the S node, you can see the NP in the denominator of the daughter NP\S node get canceled out by the NP of the other daughter node.