Sure, positive, not doubting.
"is certain" is correct and usable in written English. You can use it to emphasize that something is definite and without a doubt. For example: "It is certain that I will be attending the meeting tomorrow.".
That much is certain.
Little is certain here.
Still, nothing is certain.
"That is certain".
But nothing is certain.
Nothing is certain.
One thing is certain.
Thanks to Ludwig my first paper got accepted! The editor wrote me that my manuscript was well-written
Listya Utami K.
PhD Student in Biology, Bandung Institute of Technology, Indonesia