I would say no. If you believe what you said, you're not lying. There are grey areas here, like levels of confidence in our knowledge. A rational person believ

I would say no. If you believe what you said, you're not lying. There are grey areas here, like levels of confidence in our knowledge. A rational person believes very few things with 100% certainty, but it's not reasonable to be paralyzed by even the slightest amount of doubt and never say anything. I think a reasonable approach is to state things with some indication of your level of confidence, like: 1. Obviously sweet potatoes are yams. 2. Sweet potatoes are yams. 3. I am pretty sure sweet potatoes are yams. 4. I think sweet potatoes are yams. 5. I think sweet potatoes are yams, but I'm not sure. 6. I think sweet potatoes are yams, but I don't really know why I think that. 7. Sweet potatoes might be yams.