A pen is certainly an excellent instrument to fix a man’s attention and to inflame his ambition.

Adams’s remark treats writing not as a passive record of thought but as a tool that actively shapes it. The “pen” disciplines attention: committing ideas to paper forces selection, order, and clarity, making the mind dwell longer and more precisely on a subject. At the same time, writing can “inflame…ambition” by turning private aspirations into articulated plans and arguments—words that can be revised, strengthened, and aimed at an audience. In Adams’s world of law, politics, and pamphleteering, the ability to write well was a form of power: it could sharpen one’s own purpose and also persuade others. The line thus links literacy with self-fashioning and public influence.