The phrase "backup cause" refers to a secondary reason or explanation for something. There are various synonyms for this phrase, including "secondary reason," "additional cause," "supporting factor," "auxiliary explanation," and "supplementary justification." These synonyms can be used interchangeably with the term "backup cause" to provide clarity and variety in communication. By using synonyms, it is possible to avoid repetition and emphasize different aspects of a given situation. Whether in personal or professional communication, having a wider range of options for expressing ideas is always beneficial, and the use of synonyms can help achieve this objective.