A modifier is a word, phrase, or clause that modifies—that is, gives us information about—another word in the same sentence. For example, in the sentence, "I’m eating a vegetarian burger," the word "burger" is modified by the word "vegetarian." In longer sentences, the placement of modifiers is important for clarity. Here, Grammarly has found a confusing modifier:
The student has written the following:
Dolger discovered an ancient Mayan civilization using astronavigation.
In this sentence, the modifier is a clause, "using astronavigation." However, the sentence is unclear, because it is difficult to see what part of the sentence "using astronavigation" modifies. Did Dolger discover the civilization with "the help of" astronavigation, or did he discover a civilization that was "already using" astronavigation? The placement of the modifier affects the meaning of the sentence dramatically.
Depending on which meaning is appropriate, the student could write,
Using astronavigation, Dolger discovered an ancient Mayan civilization.
Dolger discovered an ancient Mayan civilization that used astronavigation.
The Writing Center has additional information on modifiers at Modifiers.