Scepticism is the touchstone.

(Sec.

31.) Incredulity is sometimes the vice of a fool, and credulity the defect of a man of intelligence.

The latter sees far into the immensity of the Possible; the former scarcely sees anything possible beyond the Actual.
Perhaps this is what produces the timidity of the one, and the temerity of the other.
A demi-scepticism is the mark of a feeble understanding.

It reveals a pusillanimous reasoner, who suffers himself to be alarmed by consequences; a superstitious creature, who thinks he is honouring God by the fetters which he imposes on his reason; a kind of unbeliever who is afraid of unmasking himself to himself.