The first question I hear is, "What is a Spirit Guide"? well lets try to put it into simple terms. A spirit "Guide", obviously a spirit, is a person who has lived on the Earth plane and left the physical body (died), usually, some considerable time ago, and who has decided to attach themselves and work with an individuals on this earth plain, with the sole purpose of helping them to live their life with guidance, love and understanding. (many refer to them a Guardian Angels) This does not mean that they will direct you or push you into things. We have free will and that pre-ceeds anything that an attached spirit can over come. The word "Guide" is the key, they try to guide you through difficulties, to help you make the right decisions, and watch over you in times of trouble etc.
A Medium, sees and works with a guide in an entirely different way, because they are able to communicate with their guides, an ability that we all have, but just dormant in most people. The medium is able to link with there guides in the spirit world and bring forward others spirits for the purpose of communication with loved ones, proving in the process that the physical body might die but that the sole is immortal and continues beyond that vale we call death.
How does this happen, Well, I am a person who, rightly or wrongly, likes to place things, people etc into slots. It works for me and makes things easier to work with. So following along that line:
We can, if we try hard enough, place spirit guides into three or four different categories.
a. Those who work with us in a mental capacity, that of Clairvoyance, Clairaudiance and Clairsentiance etc.
b. Those who work within the field of Philosophical Teachings, Inspirational writing or direct writing.
c. Those who work within the physical field, proving the continuation by direct and physical means such as Direct Voice, Independent Direct Voice, Materialisation etc.
d. Our fourth category I think, would be that, whereby the guides are not ever consciously heard by those they try to work through. Not seen or felt, they are what people call their Guardian Angel. The omni presence that helps those without any or little knowledge of the paranormal or the workings of spirit guides. Some describe it as an inner voice, that they don't actually hear but just sense. This sense just gives gentle nudges as people move along their pathway of life and learning, without getting actively involved in spiritual or paranormal knowledge and activities.
Of course, within all of these categories we have to accept that there are overflowing links between one category and another, and in some cases between a number of them. There will of course be sub divisions of these categories and there can be no hard and fast rules to which type of mediumship a spirit guide will portray him/herself in during the initial stages of contact. I am sure that a lot of how a spirit guide works with his medium, will depends greatly on what he has to work with. If you do not have the essential ingredients to work as a Physical Medium, it does not matter if you sit for ten years or a hundred years, without those ingredients you will not be a physical medium. That does not mean however, that you could not be a very good mental medium.
If we can just step back a little and talk more about categories, we may get a better understanding of what I mean. So lets look at Philosophical Teachings as an example. These teaching quite often come through a medium who has been entranced by his spirit guide, Entrancement in its self is the first rung of the ladder towards physical mediumship. However, it should be pointed out now, that not all trance mediums are physical mediums, and these mediums are quite happy work in the trance state. Entrancement can happen in varying degrees, from light overshadowing, where the medium is aware of all that is happening, (a bit like Clairvoyance/Clairsentiance etc.) to a deep trance state were he knows nothing of what is happening, although, this is however, apparently quite rare and when it does happen, but not always, they have usually crossed that divisional line and are working physical Mediums.