The article begins and ends with reminiscences and reflections about conversations with Myhill . The topic in the title was never far from these conversations, but remained off stage: questions about the suitability of the focus on logical languages and logical consequence, here meant in contrast to incomparable categories of propositions and proofs. The body of the article goes into cases where this focus has contributed to—and where it has distracted from more rewarding categories for—effective knowledge in mathematics. There are (...) some rules of thumb for recognizing distractions, and for doing better. (shrink)