Doubt vs Unbelief

From Alistair McGrath (quoted in Kent & Barbara Hughes, Disciplines of a Godly Family):

Doubt is natural within faith. It comes because of our human weakness and fraility. […] Unbelief is the deciion to live your life as if there is no God. It is a deliberate decision to reject Jesus Christ and all that he stands for. But doubt is something quite different. Doubt arises within the context of faith. It is a wistful longing to be sure of the things in which we trust. But it is not and need not be a problem.

In John 20:27, Jesus says to Thomas to “Stop doubting and believe” (NIV). The word behind ‘doubting’ is the word ‘unbelieving’. Therefore  ‘doubting’ is probably not the most helpful translation. So I think that McGraith is right in not having ‘doubt’ as the opposite of ‘belief’. (NASB, HCSB, ESV all go for ‘unbelief’ words.)