Someday, the mediumistic faculty will have evolved on our planet to the point where it becomes a perfect sense, common to everyone, just like that of touch, sight, or hearing .  That day is still very distant, however, and today the mediumistic faculty it is still relatively latent, so that that under most circumstances, when we speak of "mediums", we refer to those in whom, as Kardec says, the medianimic faculty is "practically applicable" and is "clearly characterized, producing well-marked results."  However, it can not go unrecognized, and therefore we make it a point to call attention to the fact here, that we are all mediums.  Remember what Kardec said, with reference to inspired mediums, that "inspiration comes to us all, from Spirits who influence us, for good or for evil, in every circumstance of our lives, and in every resolution we make, and it may therefore be truly said that, in this respect, everyone is a medium, for there is no one who has not about him his familiar Spirits, who do their utmost to suggest salutary or pernicious counsels to those with whom they are connected."

An Inherent Faculty

The reason we are all mediums is because the faculty is inherent in man.   Though not all of us have an ostensive mediumistic faculty, it is true that we all engage, consciously or not, in a continuous exchange with the invisible world and its inhabitants.  On one hand, we act as transmitters of thoughts and energies that impact the fluidic nature of our environment and can be captured by other beings, both incarnate and discarnate.  On the other hand, we are simultaneously acting as receivers, assimilating external energies from our environment and capturing the thought waves of those close-by, again both incarnate and discarnate.  

A Matter of Intuition

Question #459 of "The Spirits' Book" asks, "Do Spirits influence our thoughts and actions?", to which the Spirits replied, "To a greater extent than you suppose, they can have a significant influence on both."  It is through the kind of exchange mentioned above that Spirits are able to suggest ideas to us that we receive in the form of intuitions.  Good and friendly Spirits who wish to help us on our road of progress will suggest to us ideas that can, should we listen to them, help us to make good decisions.  This is often the case when we are pondering over a decision we must make or seeking the best way to finish a given task, and, almost as if "out of the blue", an idea comes to mind that leads us to the answer we needed.  Suggestions of positive advice, however, don't always "spring" upon us, as they may simply become interwoven into the orderly thought process through which we arrive at our decision.  

In addition to this helpful counsel, the good Spirits may also try to dissuade us from negative thought patterns or behaviors that will ultimately bring us suffering, by making appeals to our consciences and advising us to change our ways.  In our moments of discouragement, sadness, and fear, they offer comforting words that help us to overcome these painful emotions. They also  come to warn us about impending dangers and suggest ways to avoid them.  Most of us have heard a story of at least one person who, for "some unknown" reason or some strange "gut feeling", decided to drive a different route home or not get on an airplane flight, etc., only to find out that if they had, they would have been endangered in some way.  The ideas that Spirits suggest to us are not always intended for our benefit alone.  They often use the intuition of one person as a way to bring a message to another.  Again, this may be a piece of good advice, words of consolation and/or inspiration, some kind of warning, etc.

Just as good Spirits try to help each of us in the events of our daily lives, they also endeavor to inspire those human beings who work in benefit of humanity and its progress.  The great artists, philosophers, scientists, teachers, etc. who have helped assure man's progress throughout the various ages, have done so with the support and guidance of Elevated Spirits who've "selected them as instruments, suggesting to their minds the trains of thought required for their special ends." (Kardec ) 

Intuitions like the kinds mentioned above come from good and friendly Spirits that wish to help us and those with whom we come in contact.  Thoughts can also be suggested to us, however, by unenlightened or ill-intentioned Spirits who will try to trick us or influence us in harmful ways.  Instead of offering good advice or leading us from danger, they only suggest ideas and behaviors that would ultimately hurt ourselves and others, for they are jealous of us and wish for us to suffer just as they do.  Likewise they will try to create obstacles in our path that prevent us from participating in positive activities. Instead of comforting and consoling us, they cause our sorrows to deepen. Lastly, rather than dissuade us from negative attitudes and behaviors, inferior Spirits encourage and strengthen our sentiments of pride and selfishness, our feelings of animosity and vengeance, our selfish and materialistic tendencies, etc.   

The Law of Attraction

The moral and trustworthy nature of the intuitions we receive relates directly to the kinds of Spirits that they come from. So, do we have any control of the kinds of Spirits that transmit these thoughts to us?  In fact we do, and the answer stems from the Law of Moral Affinity, which says that individuals of a like moral nature attract one another, and those of a contrary moral nature repel. The kind of Spirits that accompany us and inspire us are those that are attracted to us through this moral or vibrational affinity, which depends on the kinds of thoughts we cultivate and the behaviors that are habitual to us. 

An analogy can be made to the frequencies on a radio, each band having a different style of music or other programming.  In order to hear what we prefer, we must tune our radio to the right frequency.   Likewise, Spirits of all kinds live among us and try to influence us, but in order to hear the suggestions that will help  us, we must tune our minds and our hearts, in other words our thoughts and our feelings, to the right vibrational frequency.

The Superior Spirits offer us this advice (Q # 165 of "Spirits' Book") on neutralizing  the influence of Spirits who tempt us to do wrong. They say, "Do only what is right and put all your trust in God.  By doing so, you repel and deny them power over you.  Be careful not to listen to the suggestions of any Spirit who inspires bad thoughts in you, causes trouble between yourself and others, or arouses your instinctual passions.  Distrust especially the Spirit who flatters your pride; it is attacking you at your weakest point.  This is why Jesus tells us to say, in the Lord's Prayer, 'Lead us not into temptation, but deliver us from evil.'"

In order to attract good Spirits, we must take care with our thoughts and actions, always making efforts to improve them with time and to advance in our moral and Spiritual progress.  We must seek to act with compassion, kindness, patience, respect, forgiveness, humility, optimism, etc.  We must engage often in moments of sincere prayer, in which we draw the good Spirits to our side and open our minds to their positive suggestions. As Kardec writes (#182 of "Mediums' Book"), we should "invoke [our] watchful guardian with fervor and confidence, as a Providentially-appointed friend; and if we did so, we should often be astonished at the new ideas which would arise in our minds...."

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Suggested reading:
"The Spirits' Book", Allan Kardec   Chapter XIII Spiritual Intervention in the Incarnate World
"We Are All Mediums", Odilon Fernandes (Spirit) through Carlos A. Baccelli (medium), Chapter We Are All Mediums.

Kardec, Allan. "Inspirational Mediums" and "Writing Mediums or Psychographs." The Mediums' Book. 2nd ed (1st edition FEB). Trans. Anna Blackwell (translated 1876). Ed. Livraria Espírita Allan Kardec. Brasilia-DF, Brazil:  Federação Espírita Brasileira [Brazilian Spiritist Federation}. 1986. 182-183 and 191-194.

Fernandes, Odilon (Spirit Author) / Baccelli, Carlos (Medium). "We Are All Mediums". We Are All Mediums.  Trans.Coelho, Públio Lêntulus Vicente. Votuporanga- SP, Brazil. Casa Editora Espírita "Pierre-Paul Didier". 2001 24-27. 

Simonetti, Richard "A Influencia Dos Espiritos" [The Influence of Spirits]. Espiritismo, Uma Nova Era [Spiritism, A New Era]. 2nd ed. Rio de Janeiro-RJ, Brazil: Federação Espírita Brasileira [Brazilian Spiritist Federation]. 1999. 108-119.