Final answer:
Authors use bold print or italicized words to highlight important information.
Step-by-step explanation:
The most likely reason an author uses bold print or italicized words or phrases is to highlight important information. By using bold or italicized text, the author can draw attention to key points or emphasize certain words or phrases that are significant to the overall message or theme of the text. This can help readers better understand the main ideas and arguments presented by the author.