"pretty sure" and "almost sure"
What is the (subtle?) difference bewteen these 2 sentences:
I am pretty sure
I am almost sure.

Question

Answer

To me, they mean exactly the same thing. If there is a difference in meaning, I think that "almost sure" implies more certainty than "pretty sure."

The real difference is that "pretty sure" is less formal, and while used in speaking, it would be used less often when writing.

Answer

The phrase "I am pretty sure" is stronger than "I am almost sure".