Eric Winsberg is puzzled:
I've been watching a few episodes of the BBC drama series "Foyle's War." Its a decent show, but what interests me right now is just an expression that the main character, Christopher Foyle, often uses that I had never heard before. It works like this: someone will ask him if he thinks that they ought to ____, or if he wants them to ____, and he replies "I should!"
For example "Do you want me ask all the jewelery stores in town if they've seen this necklace before?"; "I should!" or "Do you think I should check the oil in my car?"; "I should!".
Even Joseph Conrad didn’t quite get the difference between ‘will’ and ‘shall’. In a nutshell ‘will’ is optative or within the boundary of your own personal wishes; ‘should’ is normative; you are subjecting yourself to a situation or force outside yourself. Foyle as a good cop is prescinding from the personal and allowing the force of external circumstances to dictate his actions. The state of the car is the important factor as is the memory of a particular necklace. He responds to those external forces. Foyle is a righteous man.