★ A word-power guide built for the AI era — teaching you not just how to speak to people, but how to speak to AI. As AI tools become part of daily work, precise word choice is the foundation of effective collaboration.
★ Author Yamaguchi Yoji is a professor of literature at Daiichi University of Education and holds a Ph.D. in Chinese studies. His previous work won the 29th Watsuji Tetsuro Culture Award — a strong guarantee of both authority and readability.
★ The book examines the gap between “words that communicate” and “words that mislead,” exploring the culture, history, and logic behind them. It‘s not a collection of tricks — it’s a deep-dive into the fundamentals of expression.
★ Presented in an illustrated “anatomy” format, it covers business communication, prompt writing, drafting documents, and more — making word power a practical, everyday skill rather than an abstract concept.
★ “AI learns from human behavior. If you can communicate precisely with AI, you can communicate precisely with anyone.” — In an era where the line between human and machine blurs, precision is the most valuable currency in the workplace.

Communicating accurately — without being misunderstood — is difficult whether you‘re speaking to a person or an AI.
In business, unclear instructions or requests often lead to disappointing results. That’s why so many professionals are looking to strengthen their “word power” — the ability to choose exactly the right words to get the job done.
Beyond that, AI has become deeply embedded in daily work: generating images and video, proofreading and summarizing text, creating meeting minutes and presentations, writing ad copy and developing products. For all of these, the words you choose matter just as much as they do with human colleagues. Many of us have rewritten prompts again and again without getting the result we wanted — wasting time and effort in the process.
The rapid rise of AI tools has created a world where we need not only the ability to communicate with people, but the ability to communicate with machines as well.
AI learns from human behavior. Being able to communicate clearly and accurately with AI means you can do the same with anyone around you.
Written by word-power expert Yamaguchi Yoji, this book explores the difference between “words that convey meaning” and “words that cause misunderstanding,” offering guidance on how to have better conversations — with both “others” and “AI.” While focused on vocabulary for business settings, it‘s not just a technique book. It also covers the culture, history, and rules embedded in word choice — making it a resource that deepens your knowledge while improving your efficiency and work quality.

Yamaguchi Yoji was born in 1963 in Sasebo, Nagasaki Prefecture. He specializes in philology and uses AI for cataloging Chinese classics and restoring ancient Japanese texts. He currently serves as a professor at Heisei International University, a visiting professor at Takarazuka University of Medical and Health Care, a visiting professor at Shandong University in China, and a visiting professor at Daiichi University of Education. He holds a Ph.D. in Chinese studies. A graduate of Daiichi University of Education‘s Faculty of Literature and its graduate school, he has also studied at the École des Hautes Études en Sciences Sociales in France and participated in joint research with Cambridge University’s Faculty of Oriental Studies, regularly traveling between the UK and France for academic work. His research covers philology, bibliography, and Japanese history. He is the author of “Japan‘s Last Mysterious Challenge: ‘Japanese General Knowledge‘” and “The Eternal Young Worker Who Built a Career Through Expression,” which received the 29th Heisei 28 Social Education and Culture Award (General Division) from Shueisha Interactive. His other works include “How to Save Yourself When You Lack Word Power” and “1-Minute Exercises to Build a Solid Inner Logic of Expression.” He also works as a radio host, illustrator, and writer across multiple fields.

Chapter 1: Precise Word Choice for Communication with People and AI
Why You Need Word Power
Visualizing Your Message for Better Understanding
Vague Language Fails to Communicate
Breaking Down Long Sentences for Clearer Logic
Building a Complete Dialogue Chain with Context
Fine-Tuning Word Precision to Convey Your Message
Clarifying Definitions to Strengthen Your Point
Colophon: April 2026 — Yamaguchi Yoji

Chapter 2: Practical Vocabulary for Persuasion and AI Prompting
Adding Context to Improve Understanding
Using Omission and Connection for Smoother Expression
Building a Personal Phrase Bank
Anchoring Key Ideas to Guide Thinking
Speaking Directly to Build Trust
Simplifying Language to Lower the Barrier
Separating Subjective and Objective Perspectives
Guiding the Other Person to Fill in the Facts
Using Questions to Steer the Conversation
Responding Flexibly to Expand the Dialogue
Shifting Perspectives to Stimulate New Thinking
Focusing on Underlying Needs for More Effective Communication
Distinguishing Between Near-Synonyms
Adjusting Your Angle to Refine Your Expression
Column: Building Word Power from Day One ② — Writing Business Commentary

Chapter 3: Words That Cause Misunderstanding — and Better Alternatives
Using Richer Vocabulary to Convey Subtle Emotional Nuance
Avoiding Ambiguity from Indefinite Pronouns
Breaking Down Ambiguous Sentences to Cut Off Misunderstanding
Recognizing How Similar Expressions Are Perceived Differently
Reconstructing Sentences with Context for Clearer Expression
Varying Sentence Patterns to Resolve Multiple Misunderstandings
Combining Vocabulary Layers to Eliminate Ambiguity
olumn: Building Word Power from Day One ③ — Writing Professional Reports

Chapter 4: Vocabulary-Building Exercises
Practice: Words of Gratitude and Sympathy
Practice: Words of Apology
Practice: Words for Making Invitations
Practice: Words for Declining Requests
Practice: Words for Making Commitments
Practice: Words for Warnings and Notices
Practice: Words for Emails
Practice: Words for AI Prompts
Afterword