by choice

形容词 by choice:

1. not by chance

副词 by choice:

1. with intention; in an intentional manner
   同义词：intentionally, deliberately, designedly, on purpose, purposely, advisedly, by design

1. He has grown interested in graphic education first by force of circumstance but later by choice.
   开始由于形势所迫，但后来出于自己的选择，他逐渐对书画教育感兴趣起来。