Greetings from the Abyss

Actually, evoking is the official term for "summoning" invoking is asking an entity for it's presence.

If evoking is summoning, then how is invoking asking for it's presence?

To summon is to request an appearance, so it could be argued that it's the same thing. Although we know it's not.

http://www.glasstemple.com/basics/index.php?conjure=invoke
http://en.wikipedia.org/wiki/Invocation

i have to agree with rashnu he has noted a few things that
are true
and yes sigils are not necessary
i just started to work with sigils this was not always the case!

also there is no way we can know all the names of the demons some are named but as we know some go buy diferent names and some have not been named (meaning that in diferent relegions demons have many names)

i want to make a simple explanation!

how would it be if you are working with a demon but don't know it's name! do you think he will come to you and say
hello my name is xxxxx or ******** no this will not happen
but there is also another thing!
some of us the ones who are new to this
are working and learning about the craft so yes we learn first about their names ect!!

invoker i think you can take what rashmu is telling as good
criticism!

ok i am not saying that you should do what i say of what he say's
i am only trying to point out that
rashmu has pointed some things about this matter!!

With invocation the spirit in question is invoked into your circle or temple. No protective devises are used against it, and it is done by request, not force. This also may happen unintentionally when a god is addressed in prayer or other devotional practices and decides to talk back.

With evocation however the spirit is summoned by force or by request, using various god names and magical words. The spirit is then forced or channeled to appear inside a device specially made for this purpose, mostly a round black mirror mounted in a triangle with various god names written on the sides of the triangle. This evokes the spirit inside the round black mirror and the triangle imprisons the spirit within it. Then you can ask the spirit to do your bidding.

So where with invocation the spirit is asked freely to come, and can do as it pleases. With evocation however the spirit is summoned forcefully and contained within a special devise. It should be obvious that higher spirits shouldn't be evoked, since it will prove hard to contain them and they will not be pleased by it.

Often invocation involves allowing the invoked entity into one's own mind or even body and converse with them this way, or even allow them to take over and speak through the practitioner. There are several terms for that, including horseing (the spirit rides the practitioner, used in a voodoo/santeria/hoodoo context) and aspecting (=experiencing aspects of the evoked entity directly). Some magicians use the term invocation only when such contact is included, no matter weather thee invoked entity was asked or brought on forcefully, others stress the aspect of the entity's freedom to come and go. Such contact may be called possession when the practitioner looses control over the process.