Two Principal Orders

Physical Mediums : Those who have the power of obtaining physical manifestations.

Intellectual Mediums: Those whose mediumistic faculty is most conducive to receiving and transmitting intelligent communications.

"All the other varieties belong to one or the other of these two categories; some belong to both.  If we analyze the different manifestations obtained through medianimic influence, we shall see that there is, in all of them, a physical effect, and that, combined with the physical effect, there is usually an intelligent effect.  It is sometimes difficult to establish a line of demarcation between the two; but this is of no practical consequence.  We include, under the denomination of intellectual mediums, those who are especially able to serve as intermediaries for the transmission of regular and continuous communications." (Kardec,  "Mediums' Book", Ch XVI #187)