该句表示确信，也可以说"beyond doubt" "no doubt" 。
1. Without a doubt these theories were all wrong.
2. No doubt I learned a lot from him.
3. They convinced me that Harry was, beyond the possibility of doubt, innocent.
A: Who is your favorite music composer?
B: I don't have one single favorite, but these days I listen to a lot of Chopin.
A: Then you must despise such modern music as rock?
B: Without doubt, rock is trash.