Phân biệt Illusions/delusions, astronomy/astrology…

Phân biệt Illusions/delusions, astronomy/astrology, cynicism/skepticism, psychiatry/psychology

There are many words that are sometimes used incorrectly in ordinary speech by sloppy or uneducated native speakers where distinctions in meaning should be kept in mind. Here are four of these:  illusion versus delusion, astronomy versus astrology, skeptical versus cynical, and psychiatry versus psychology.


Both of these words refer to something seen that is not really there, and, by extension, an idea or notion that is not real.  The difference is not particularly subtle; an illusion is something one sees but is intellectually aware that it is not really there.  One believes in the reality of a delusion.  Delusional people are therefore seen by others as mentally deranged–perhaps only a little on this one issue, perhaps flat-out insane.  We say the sky is blue, but this is an illusion.  We know the “blueness” is in our heads, not in the sky.  What comes from the sky are light waves of a certain frequency that our mind interprets as blueness.  This points out another difference between illusion and delusion–illusions have an external, more basic physical cause, while delusions are entirely mental.  We say that the sun “rises” in the morning.  Again, this is an illusion–what really happens is that the Earth rotates.  A delusional person might insist that the sun is really the thing that moves.


Astronomy is the scientific study of objects outside the Earth (and also of the Earth too when it is viewed as an object in the Solar System).  It is a branch of science, mostly of physics.  Astrology is not a science but the superstition that tries to predict the future based on the position of the planets in the sky.  The astronomer tries to explain why the universe is as we observe it by observing it in detail and applying rational scientific methods to what is observed.  The astrologer tries to discern fates by making applying traditional maxims to the positions of the planets.


The cynic is an unfortunate person who arrogantly will not believe anything he or she does not want to believe, regardless of the evidence.  The skeptic is a rational person who may still be somewhat arrogant in refusing to believe things on faith but can be persuaded if one can present a convincing case.  The cynic uses the fact that nothing can be proven absolutely, the skeptic understands this too and reserves acceptance until a good, rational case is presented.  We sometimes hear the expression “healthy skepticism,” which is redundant, since most people will agree that all skepticism is healthy–that not to be skeptical is to be gullible.  On the other hand, cynicism is never healthy.


Psychiatry is a branch of medicine that deals with the human mind–usually diseases of the mind that manifest in irrational behavior.  Psychology is an academic subject, the science of the human mind, and tends to be less interested in insanity and more interested in mental phenomena such as perception, emotion, belief, personality, and so on.  The psychiatrist has a medical degree (M.D.) and a medical practice; the psychologist generally teaches in a university and has an academic degree (Ph.D.).

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