Definitions are not especially important, and we generally should not begin conversations by discussing them. It's better to begin with a statement of a problem to address, and a short explanation addressing it. Then meanings of words can be discussed if, and only if, there is some ambiguity or confusion hampering the discussion. Here are some reasons not to begin with definitions:
- In a discussion, we have some topic (say, physics) we want to talk about. Any time spent on definitions isn't spent directly working on what we're interested in.
- Definitions can never be perfect. Some people think they can start with definitions, and get them out of the way for the whole conversation. But actually they may need to be revisited and revised.
- We only need a certain amount of precision to solve the problem we're trying to solve. If we start with definitions, we might overdo it and pursue excess precision. If we start with the topic itself, and periodically revisit definitions to increase their precision when we have some specific reason we believe that will be beneficial then we won't waste our effort.
- It's hard to predict in advance exactly which words we may find useful to define or not.
- Arguing about terminology is a waste of time. It's not important which string of characters is mapped to which concept.
- We can never define all our terms. Some terms must be left undefined. Attempting to define all our terms leads to regress or circularity.
- People never understand each other perfectly, and defining words doesn't change that. Definitions do not fundamentally change the nature of conversation by getting everyone on the same page. They can sometimes help do that; other things can too (such as saying on-topic statements).
- It's not obvious what the definitions of words should be. We need to know something about the topic under discussion before we can determine what word definitions will be helpful. Definitions are better added later when we understand more.