How to tell if a phrase/word is a metonymy, synecdoche, or neither?

The difference between metonymy and synecdoche is that in metonymy, the term you are usin is linked to the thing you mean, but not directly. In synecdoche, part equals whole and thing equals concept. There is a theory that ALL written language is metonymy..as a word can only be representative by the idea of the thing it is ntended to portray. Perhaps these phrases are both? The difference between them is way too subtle to tell for sure. Good luck, and I think your question is a wonderful one, even in spite of the subject matter. It's nice to see an intelligent question!