Why Diagram Grammar?
In grammar books, “subject,” “predicate,” and “object” are often just abstract terms. But in a diagram, they become visible structures—lines, positions, directions. Instead of memorizing rules, you can literally see how a sentence works.
The Reed–Kellogg system is a tool for making grammatical structure visible.
Its core principle is simple: break every sentence into functional units, and connect them with lines. The direction and placement of each line express the syntactic relationships.
I. The Sentence Backbone: Start with Subject and Predicate
No matter how complex a sentence appears, its core is always a subject + predicate structure.
In Reed–Kellogg, this is represented with a single horizontal line:
Subject | Predicate
This line is called the baseline. A vertical line cuts through the middle—subject goes on the left, predicate on the right.
Example: Dogs bark. Diagram:
Dogs | bark
No matter how advanced the sentence becomes, it always builds upon this structure.
II. Add Objects and Complements: Expanding the Predicate
If the verb is transitive (like “play” or “know”), it takes a direct object. In the diagram, draw a short vertical line (that doesn’t cross the baseline) after the verb.
Example: Children play games. Diagram:
Children | play | games
If the verb is a linking verb (like “be,” “seem,” “become”), it takes a subject complement—a noun or adjective describing the subject. In this case, use a backslash (\
) to indicate that the complement refers back to the subject.
Example: She is happy. Diagram:
She | is \ happy
These two structures form the second layer of the sentence’s skeleton.
III. Add Modifiers: Growing the Sentence “Branches”
1. Adjectives and Adverbs
- Adjectives modify nouns → use a slanted line below the noun
- Adverbs modify verbs, adjectives, or other adverbs → also use slanted lines
Example: The big dog barked loudly.
- “the” and “big” modify “dog”
- “loudly” modifies “barked”
Each modifier connects to its word with a diagonal line in the diagram.
2. Prepositional Phrases
Prepositional phrases are compound modifiers, often indicating place, manner, or time. They typically come after nouns or verbs.
Diagram steps:
- Draw a diagonal line from the word being modified
- Write the preposition on this slanted line
- Draw a horizontal line to hold the object of the preposition
- Add modifiers to the object if necessary
Example: She ran across the field.
In the diagram, “across” appears on the slanted line, leading to “the field.”
IV. From Simple to Complex: Understanding Sentence Construction
Even complex sentences follow the same pattern: core structure + modifiers, though some modifiers may be full clauses.
1. Coordination (Multiple Subjects, Verbs, or Objects)
- Use dotted lines to connect coordinated elements
- Label conjunctions (and, or, but) on the line
Example: Tom and Jerry run and jump.
In the diagram, both subjects and both verbs are shown as paired elements, joined by dotted lines.
2. Subordination (Dependent Clauses)
Subordinate clauses are embedded mini-sentences that function as nouns, adjectives, or adverbs within the main sentence.
- Adverbial clauses: connect from the verb with a dotted diagonal line
- Adjective clauses: connect from the noun they modify
- Noun clauses: use stepped lines, taking the place of a noun
Example: Because it rained, we stayed inside.
- Main:
we | stayed
- Clause:
it | rained
- “because” labeled on a dotted line linking the two
V. Drawing a Diagram: A 4-Step Process
You can analyze almost any sentence with these four steps:
Step 1: Identify the Core
- Who is acting? → Subject
- What’s the action/state? → Predicate
- Is there an object or complement?
Step 2: Draw the Base
- Draw the horizontal baseline
- Use a vertical divider between subject and predicate
- Add object or complement if present
Step 3: Add Modifiers
- One-word modifiers → diagonal lines
- Prepositional phrases → diagonal + platform
- Clauses → mini-diagrams connected by dotted or stepped lines
Step 4: Check Structure
- Does every modifier point to the correct word?
- Are conjunctions and subordinators clearly labeled?
VI. Sentence Pattern Practice
Beginner Patterns:
| Sentence | Structure | | -------------------- | ---------------------------------- | | The cat sleeps. | Subject + intransitive verb | | Mary reads books. | Subject + transitive verb + object | | The weather is cold. | Subject + linking verb + adjective |
Intermediate Patterns:
| Sentence | Type | | ------------------------------------------------ | ----------------------------- | | The large dog quickly ran through the park. | Adverb + Prepositional Phrase | | She gave her friend a beautiful gift. | Double Object | | Reading books and writing essays improve skills. | Gerund Subject + Coordination |
Advanced Patterns:
| Sentence | Type | | ------------------------------------------------------------------------- | -------------------------- | | The student who studied passed the exam the professor had written. | Nested Adjective Clauses | | Although it rained, runners trained because the marathon was approaching. | Multiple Adverbial Clauses |
VII. Common Pitfalls to Avoid
| Error Type | Example Mistake | How to Fix | | ----------------------- | -------------------------------- | ----------------------------------- | | Misplaced Modifier | Adverb connected to noun | Verify modifier function | | Misidentified Structure | Complement mistaken as object | Clarify role by sentence function | | Wrong Clause Attachment | Clause linked to wrong noun/verb | Analyze the clause separately first |
Conclusion:
Grammar Isn’t Just Rules—It’s Spatial Design
Grammar isn’t abstract. It lives in the physical arrangement of every sentence. Reed–Kellogg diagramming turns language into a spatial map.
Start with the main line. Layer by layer, add the branches. Draw the diagram—and you’re literally uncovering the logic hidden inside the sentence.
Next step: choose a sentence you know well, draw it out, and see how the structure unfolds. With each diagram, your grammar sense will sharpen.