By Donald Michael Kraig
[Snip] The terms “invocation” and “evocation” are often used interchangeably by people who are either not magickally inclined or are consciously seeking to confuse their followers. However, they have specific meanings and it’s important to understand the difference.
Invocation means to bring something into you. When you invoke something, you are taking the qualities of what you invoke into yourself. For example, you might want to invoke elemental Fire to give yourself more energy and drive, or to help you stay awake and alert during long drives or all-nighter study sessions. A classic example of invocation is the Wiccan rite known as Drawing Down the Moon. In this ritual the Goddess is brought into the physical body of the worshiper and can then communicate with others and enjoy the physical world. A person working as a New Age type of Channel invokes one or more entities.
Evocation means to draw something forth. Thus, if you wanted to communicate directly with a spirit, angel, archangel, etc., you would evoke that spirit. Sometimes the evocation can be so powerful that you can see the entity evoked, or at least see it in a crystal, a magick mirror, or possibly in the smoke of incense. Even if it cannot be seen, it may be felt or experienced through another sense, such as through hearing.