How to Diagram a Sentence (Reed-Kellogg Method)
Diagramming a sentence forces you to commit to an answer. You cannot draw the diagram until you have decided what the subject is, which word is the main verb, and what every other word is doing hanging off of them. That is exactly why English teachers still assign it: a Reed-Kellogg diagram turns invisible grammatical structure into lines on a page, and a wrong analysis shows up as a line that has nowhere to go.
The mechanics are not the hard part. A horizontal baseline, a few vertical bars, and some slanted lines underneath will carry almost any sentence. The hard part is the grammar, deciding whether a word modifies the subject or the verb, where a prepositional phrase attaches, and how to split a compound sentence. This guide walks through the Reed-Kellogg system and then shows how to lay out a clean, labeled diagram with the SciDraw AI Sentence Diagram Generator.
The Reed-Kellogg baseline splits the subject from the predicate with a vertical line that cuts through the baseline.
Quick Answer
A Reed-Kellogg diagram places the core of the sentence on a horizontal baseline: the subject, the verb, and any direct object or complement, separated by vertical lines. Everything that modifies those core words drops onto slanted lines beneath them. Prepositional phrases hang below the word they modify, conjunctions sit on dashed lines linking the parts they join, and a compound sentence becomes two baselines connected at the verbs. The position of a line is the claim: where a word sits is its grammatical job.
| Diagram part | What goes there | How it is drawn |
|---|---|---|
| Baseline | Subject | verb | object or complement | Horizontal line, split by vertical bars |
| Subject–verb divider | Between subject and verb | Vertical line through the baseline |
| Verb–object divider | Between verb and direct object | Vertical line resting on the baseline |
| Verb–complement divider | Before a subject complement | Line slanted back toward the subject |
| Modifiers | Adjectives, adverbs, articles | Slanted lines under the word modified |
| Prepositional phrase | Preposition + its object | Slanted line down, object on a horizontal line |
| Conjunction | and, but, or | Dashed line between the joined elements |
| Compound sentence | Two independent clauses | Two baselines joined by a dashed line at the verbs |
The single rule that ties it together: a word's position carries its function. A modifier under "dog" describes the dog; the same word under the verb describes the action. Move the line and you have changed the grammar.
How a Reed-Kellogg Diagram Is Built
Every diagram starts from the baseline, which holds only the skeleton of the sentence. You find the simple subject and the simple verb and write them on one horizontal line, separated by a vertical line that cuts all the way through. A direct object goes to the right of the verb behind a second vertical line that sits on the baseline rather than crossing it. If instead the verb is a linking verb followed by a complement ("She is a teacher"), the divider slants backward toward the subject, a visual reminder that the complement renames the subject rather than receiving an action. This core is the whole foundation, because every other word attaches to one of these three slots.
Modifiers come next, and they live below the line. Adjectives, articles, and adverbs each ride on a slanted line drawn down from the word they modify, so "the" and "big" both slant down from "dog," while "quickly" slants down from "ran." A prepositional phrase extends this further: the preposition slants down from whatever it modifies, then bends into a horizontal line carrying its object, with that object's own modifiers slanting down again. So "the dog in the yard barked loudly" produces a baseline of just dog | barked, with "the" under dog, "loudly" under barked, and the phrase "in the yard" hanging beneath "dog."
Conjunctions and compound structures are the last layer. When "and," "but," or "or" joins two subjects, verbs, or objects, those elements stack in parallel with the conjunction on a dashed line between them. A full compound sentence ("The bell rang and the students left") becomes two complete baselines drawn one above the other, joined by a dashed line that runs between the two verbs and carries the conjunction. A complex sentence works the same way, but the dashed connector carries the subordinating word ("because," "when," "although") and links the dependent clause to the word it modifies in the main clause.
Common Mistakes
Mistake 1: Putting the complete subject on the baseline
The baseline holds the simple subject and simple verb only, never the whole phrase. In "The tired old dog slept," only "dog" and "slept" sit on the line; "the," "tired," and "old" all slant down beneath "dog." Writing the full noun phrase on the baseline collapses the modifier structure the diagram is supposed to reveal.
Mistake 2: Confusing a direct object with a subject complement
A direct object receives the action and sits behind a straight vertical line ("She kicked | the ball"). A subject complement follows a linking verb and renames the subject, so its divider slants back toward the subject ("She is \ a teacher"). Drawing both the same way hides the difference between an action and a description, which is usually the exact point of the exercise.
Mistake 3: Attaching a prepositional phrase to the wrong word
A prepositional phrase has to hang beneath the word it actually modifies, and that is a grammar decision, not a drawing one. In "I saw the man with the telescope," attaching "with the telescope" under "saw" versus under "man" diagrams two different meanings. The lines cannot resolve the ambiguity for you; you have to decide what the sentence means first.
Mistake 4: Flattening a compound or complex sentence onto one baseline
Two independent clauses need two baselines, and a subordinate clause needs its own line linked back by a dashed connector. Cramming everything onto a single baseline turns "The bell rang and the students left" into a tangle, and loses the very structure (coordination versus subordination) that the diagram exists to show.
How to Diagram a Sentence with SciDraw AI
SciDraw AI is a drawing tool, not a grammar checker. You do the parsing, deciding the subject, the verb, the objects, and what modifies what, and SciDraw AI draws and labels the Reed-Kellogg diagram from your description. It lays out the baseline, the dividers, and the slanted modifier lines, and produces a clean figure you can drop into a worksheet, a slide, or a handout. Because it renders the structure you describe, you should always review the grammatical analysis yourself before you rely on it.
Open https://sci-draw.com/sentence-diagram-generator and describe the sentence in plain language. You will get the best results when you include:
- the full sentence you want diagrammed,
- the simple subject and the main verb,
- any direct object or subject complement,
- which words modify which (adjectives, adverbs, prepositional phrases),
- any conjunctions and whether the sentence is compound or complex.
For a simple sentence, a prompt that works well:
Diagram the sentence "The small dog barked loudly" in Reed-Kellogg style. Put "dog" and "barked" on the baseline with a vertical divider. Slant "the" and "small" down under "dog", and "loudly" down under "barked".
For a sentence with a prepositional phrase and a direct object:
Diagram "The student read a book in the library" in Reed-Kellogg style. Baseline is "student | read | book". Put "the" under student, "a" under book, and hang the prepositional phrase "in the library" beneath "read".
And for a compound sentence:
Diagram the compound sentence "The bell rang and the students left" in Reed-Kellogg style. Draw two baselines, "bell | rang" and "students | left", and join the two verbs with a dashed line carrying the conjunction "and".
A vague prompt like "diagram this sentence" forces the tool to guess the parse, and a guessed parse is the one thing you do not want in a grammar lesson. Spelling out the subject, verb, and every attachment gets you a figure that matches the analysis you intend to teach.
For a classroom worksheet, a clean labeled baseline with the modifiers in place is usually enough. For a slide or a printed handout, ask for legible labels and enough spacing that the slanted lines stay readable once the figure is resized.
Work out the grammar once, then get a clean, labeled diagram with the SciDraw AI Sentence Diagram Generator.
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