Useful language

Opinions, Preferences:

I think..., In my opinion..., I'd like to..., I'd rather..., I'd prefer..., The way I see it..., As far as I'm concerned..., If it were up to me..., I suppose..., I suspect that..., I'm pretty sure that..., It is fairly certain that..., I'm convinced that..., I honestly feel that, I strongly believe that..., Without a doubt,...,

Disagreeing:

I don't think that..., Don't you think it would be better..., I don't agree, I'd prefer..., Shouldn't we consider..., But what about..., I'm afraid I don't agree..., Frankly, I doubt if..., Let's face it, The truth of the matter is..., The problem with your point of view is that...

Giving Reasons and offering explanations: To start with, The reason why..., That's why..., For this reason..., That's the reason why..., Many people think...., Considering..., Allowing for the fact that..., When you consider that...