( Give him an inch and he'll take a yard.=(If you give him an inch , he'll take a yard
Spare the rod and spoil the child.=If you spare the rod, you will spoil the boy.
There is a type of conditional clause , used in sentences of a proverbial nature , where the condition is expressed in the form of a command
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I received my wages yesterday , so that I can now pay what I owe you.
He was speaking very quietly , so that it was difficult to hear what he said.
This constructon differs from the similar construction introducing a clause of P urpose , in that it is not followed by may ,might or should
المرجع A Comprehensive English Grammar