A system for proofreading a text document and automatically detecting and replacing text words in the document which exceed a predetermined understandability level for the documents intended audience. Text words and synonyms are stored in a dictionary which includes an understandability code for each word based statistically on textbook grade levels. The operator enters a grade level code into the system for the intended document audience. The system scans the document for words which exceed the desired grade level, highlights those words on the system display and prompts the operator with synonyms which can be used to replace the highlighted word. The operator may select a desired replacement synonym by placing the system cursor underneath the word and depressing and enter key from the system keyboard.