I'm not sure what you mean by "positive". I think you mean that something is certain or uncertain? Either way, you can use both "traces" and "dates". When you add "can be" to the sentence, it sounds less certain. "The cathedral can be dated back to the 18th century." - Less certain. "The cathedral dates back to the 18th century." - More certain. "The cathedral can be traced back to the 18th century." - Less certain. "The cathedral traces back to the 18th century." - More certain. All of these are stated as fact. If you are simply unsure of something, you would use additional qualifiers. "The cathedral probably dates back to the 18th century." This is stated as something with is most likely true, but might not be.