Section — Slater, Manual of Moral Theology
Section II. Idolatry
The sin of superstition is also committed by giving divine honour to false gods. This is done by idolatry, divination, vain observance, and magic.
p. i, 141
By material idolatry divine worship is given to a creature through fear or for some other reason merely externally, without any intention of honouring it as God. It is a grave sin, for it is directly against the obligation of making external profession of the faith, and contains the grave malice of a lie in matters of religion.
p. i, 141
Formal idolatry is perfect or imperfect. The former consists in honouring a creature as God, falsely thinking it to be God. The latter knowingly honours a creature as God, without any excuse of ignorance, out of hatred towards him, or wishing to obtain something thereby. Both are grievous mortal sins, but the latter is the more grievous on account of the greater knowledge and malice.
p. i, 141