不定式用作独立成分通常为一些固定短语，其中一个用法就是表真诚：

■to be fair 说句公平话

To be fair, he wasn’t entirely to blame. 说句公道话，这不能全怪他。

■to be (perfectly) frank 坦率地讲

To be perfectly frank, you’ re a bad driver. 非常坦率地说，你车开得不好。

To be frank with you, I don’t like the way you talk. 坦白说，我不喜欢你说话的方式。 

■to be honest说老实话，老实说

To be honest, I just don’t like him. 说老实话，我就是不喜欢他。

To be honest, I don’t think we have a chance of winning. 说实话，我认为我们没有获胜的可能。

■to do sb justice 说句对某人公道的话

To do her justice, we must admit that she did deserve to win. 说句公道话，我们得承认她应该获胜。

■to tell (you) the truth 老实说，说真的，说实话

To tell the truth, I fell asleep in the middle. 老实说，我在中间睡着了。

To tell you the truth, we don’t have a very good opinion of him. 说真心话我们对他的印象不太好。