It is certain that they will arrive before the party begins. We are certain to have a good time. It's cold outside. ~ Indeed it is! That was a lovely party, indeed. May I help myself to some more cake? ~ By all means; we have plenty. I wasn't invited to the party. Apparently Sally is still angry with me.
It is certain that they will arrive before the party begins. [There is no doubt.] We are certain to have a good time. [We have no doubt.] It's cold outside. ~ Indeed it is! [Yes, very cold.] That was a lovely party, indeed. [Yes, very lovely.] May I help myself to some more cake? ~ By all means; we have plenty. [No problem!] I wasn't invited to the party. Apparently Sally