Reed–Kellogg sentence diagram

A sentence diagram is a pictorial representation of the grammatical structure of a sentence. The term "sentence diagram" is used more when teaching written language, where sentences are diagrammed. The model shows the relations between words and the nature of sentence structure and can be used as a tool to help recognize which potential sentences are actual sentences.

An early attempt at creating "a complete system of diagrams" for syntax analysis was made by grammarian S. W. Clark in his 1860 volume A Practical Grammar: in which Words, Phrases, and Sentences Are Classified According to their Offices and Their Various Relations to One Another. The system, which involves linking together "balloons" of words, failed to catch on. Educators Alonzo Reed and Brainerd Kellogg would soon create what was to become the definitive system for traditional sentence diagramming in their 1877 work Higher Lessons in English. This "Reed–Kellogg system" was developed to teach grammar to students through clear visualization. It lost some support in the 1970s in the US, and it is not widely used in Europe. It is considered "traditional" in comparison to the parse trees of academic linguists.

Simple sentences in the Reed–Kellogg system are diagrammed according to these forms:

The diagram of a simple sentence begins with a horizontal line called the base. The subject is written on the left, the predicate on the right, separated by a vertical bar that extends through the base. The predicate must contain a verb, and the verb either requires other sentence elements to complete the predicate, permits them to do so, or precludes them from doing so. The verb and its object, when present, are separated by a line that ends at the baseline. If the object is a direct object, the line is vertical. If the object is a predicate noun or adjective, the line looks like a backslash, \, sloping toward the subject.

Modifiers of the subject, predicate, or object are placed below the baseline:

Modifiers, such as adjectives (including articles) and adverbs, are placed on slanted lines below the word they modify. Prepositional phrases are also placed beneath the word they modify; the preposition goes on a slanted line and the slanted line leads to a horizontal line on which the object of the preposition is placed.

These basic diagramming conventions are augmented for other types of sentence structures, e.g. for coordination and subordinate clauses.

Reed–Kellogg diagrams reflect, to some degree, concepts underlying modern parse trees. Those concepts are the constituency relation of phrase structure grammars and the dependency relation of dependency grammars. These two relations are illustrated here adjacent to each other for comparison, where D means Determiner, N means Noun, NP means Noun Phrase, S means Sentence, V means Verb, VP means Verb Phrase and IP means Inflectional Phrase.