It's all to do with the level of certainty.
For example, I'm pretty sure that there isn't a pink elephant sitting quietly in the room next to me. Of course, to be 100% sure I would have to go and take a look but I feel on pretty safe ground saying that I suspect there isn't.
For example, I'm pretty sure that there isn't a pink elephant sitting quietly in the room next to me. Of course, to be 100% sure I would have to go and take a look but I feel on pretty safe ground saying that I suspect there isn't.