In a recent post Ellie gave a detailed description of what Blake meant by Doubt.
This post points to some of the sources. As everyone knows Blake was more (very much more) indebted to the Bible than to any other documents. Here are some passages of scripture showing the particular places where the biblical meaning of the word, doubt, remarkably resembles the way Blake used it:
(These quotes came from the excellent King James Bible published by the University of Michigan.)
-  Forasmuch as an excellent spirit, and knowledge, and understanding, interpreting of dreams, and shewing of hard sentences, and dissolving of doubts, were found in the same Daniel, whom the king named Belteshazzar: now let Daniel be called, and he will shew the interpretation.
-  And I have heard of thee, that thou canst make interpretations, and dissolve doubts: now if thou canst read the writing, and make known to me the interpretation thereof, thou shalt be clothed with scarlet, and have a chain of gold about thy neck, and shalt be the third ruler in the kingdom.
-  And immediately Jesus stretched forth his hand, and caught him, and said unto him, O thou of little faith, wherefore didst thou doubt?
-  Jesus answered and said unto them, Verily I say unto you, If ye have faith, and doubt not, ye shall not only do this which is done to the fig tree, but also if ye shall say unto this mountain, Be thou removed, and be thou cast into the sea; it shall be done.
-  And when they saw him, they worshipped him: but some doubted.
-  And seek not ye what ye shall eat, or what ye shall drink, neither be ye of doubtful mind.
-  Now when the high priest and the captain of the temple and the chief priests heard these things, they doubted of them whereunto this would grow.
-  Now while Peter doubted in himself what this vision which he had seen should mean, behold, the men which were sent from Cornelius had made inquiry for Simon's house, and stood before the gate,
-  Arise therefore, and get thee down, and go with them, doubting nothing: for I have sent them.
-  And the spirit bade me go with them, nothing doubting. Moreover these six brethren accompanied me, and we entered into the man's house:
-  Him that is weak in the faith receive ye, but not to doubtful disputations.
-  And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin.
-  I will therefore that men pray every where, lifting up holy hands, without wrath and doubting.