Surely vs certainly

[Daisy]

Hi, everybody! Here are two sentences:
1. I would surely have noticed more if I had realized the importance of the sea to us human beings.
2. New sources of energy can certainly be obtained from the sea.
It is said that each is appropriate for its sentence. But why? I'm not clear about their difference need your help.

[Alan]

Hi Daisy,

Surely in your sentence is used in a way to ask for confirmation: I would surely (wouldn't I?) have noticed .....

Certainly in your sentence indicates that it's clear/that it's definite: can certainly (there is no doubt) be obtained ....

Alan
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English as a Second Language
You can read my ESL story Indirect Speech