Donald J. Cram has written:

'Fundamentals of carbanion chemistry'

Carbonium is synonym to carbocation = carbon atom in a compound that has lost a single electron and therefore bears a positive charge (+1).

Carbanion in the other hand is a carbon atom in a compound that has gained an electron and therefore bears a negative charge (-1)

CH4 --> 3H+ + CH3- : monohydrogen carbane (carbanion)

Actually the base eg OH group attacks on the alpha Hydrogen atom thus releasing the carbanion and itself forming water. The carbanion further reacts with another aldehyde molecule forming methoxide ion which reacts with water to form aldol product and releases the OH group.

The conjugate base of methane (CH4) is the methyl carbanion (CH3-). Because methane is an extremely weak acid, the methyl carbanion is an EXTREMELY STRONG BASE.

Compounds like methyl lithium (CH3Li) are, in fact, considered organometallic superbases and will violently deprotonate even the weakest acids (such as water and ammonia).