Antonyms for the phrase "without rhyme or reason" include words like logical, rational, sensible, coherent, well-grounded, reasonable and wise. These words imply a clear and systematic thought process, as opposed to the absence of any such method or rationale. They suggest an approach that is planned, well thought out, and based on solid reasoning or evidence. Antonyms can help to create contrast and to illustrate the meaning of a particular phrase, allowing readers to better understand the intended meaning. In this case, antonyms for "without rhyme or reason" can highlight the importance of clear and rational thinking in decision-making and problem-solving.