Diagram a sentence using a straight line with space for the subject, verb and complements. Use diagonal lines that branch off the main line for modifiers, including adjectives, adverbs and prepositions.
Begin the diagram with a horizontal line for the main components of the sentence. Draw a vertical line halfway across the original line. Write the subject of the sentence on the left of the vertical line and the verb on the right. If the subject is preceded by an article adjective or another adjective, such as "the" or "big," place each item on an individual slanted line under the subject. Place adverbs on a slanted line under the verb.
Place prepositional phrases by drawing a line that slants first and then branches into a straight line under the part of speech they modify. Write the preposition on the slant but the object of the phrase on the straight line. Any articles go under the object on an additional slanted line. Direct objects are placed after the verb with a vertical line that only touches but does not cross the original horizontal line. If there is an article before the direct object, it is also placed underneath on a slanted line.