Aliens - Trope

Aliens:

• Life forms that are not human and do not originate on Earth.
• There are stories that feature non-human sentient species that are from newly discovered regions of the Earth - center of the Earth, bottom of the ocean, etc. Their designation as alien species is debatable  - if they originated on Earth don’t we share DNA and are therefore related? Don’t they belong here too? As the Earth gets more thoroughly explored and as science advances, these species are less likely to come up in SF.
• Often imagined by referring to and mixing up the known - ant-like, mind like a computer, moral system similar to the Japanese Bushido code. it’s very difficult to imagine something truly alien with a mind filled with the familiar. An author has to be very careful with her world-building, character building, and plotting to come up with the truly alien. some of the most alien aliens are hardly described at all, leaving it all up to the reader’s imagination.
• Might or might not be sentient.  There are many alien pets in SF, for instance.  Not to mention all the other-planetary biospheres filled with alien species.
• Often serve as a way to examine ourselves – either by seeing ourselves through the alien’s eyes, or by using the alien to highlight the more “alien” aspects of our selves.  Sometimes also serve as a metaphor for alienation.
• Also used to emphasize our similarities in a society that often talks about our differences.
• A story might be human-centric or alien-centric.  Might not involve humans at all.
• In any story involving humans and another species, humans are one of 2 alien races; it depends on your point of view.
• The terms “species” and “race” are both used.  Also called extraterrestrials (ETs). The scientific prefix is “xeno” as in xenobotany and xenolinguistics.
• Common tropes involving aliens:
• First Contact – When 2 or more species alien to each other meet for the first time.  Might or might not involve humans
• Galactic civilization/confederation – A whole confederation/or civilization of alien specie(s) out there that humanity has to figure out their place in and deal with.  Sometimes something we helped start, like Star Trek’s Federation, sometimes something that long preceded us.
• Invasion – Aliens invading the Solar System, or humans invading alien space. Usually involving war, though I’ve read stories with peaceful, if not friendly, invasions.
• Remnants – Remnants of a very old, usually very advanced, extinct alien civilization that are a major factor in the story.  Usually their technology comes into play.  Sometimes the civilization is not as extinct as we thought.
• Aliens among us - Aliens living on Earth with humanity, either openly or secretly.
• Alien POV - Stories told from an alien point of view, usually looking at humanity, sometimes in the form of one human.
• Human Unification - Aliens serve as a threatening “other” to promote human unification – the enemy of my enemy is my friend.

Books/Series
Gateway series by Frederik Pohl (Remnants)
Doona series by Anne McCaffrey (First Contact)
Contact by Carl Sagain (First Contact)
Cuckoo’s Egg by C.J. Cherryh (First Contact)
Stranger in a Strange Land by Robert Heinlein (Aliens)
Ring of Swords by Eleanor Arnason (Aliens)
Tripod series by John Christopher (Alien Invasion)
Liaden Universe by Sharon Lee & Steve Miller (Galactic Civilization, Alien POV)
Sector General by James White (Galactic Civilization, Alien POV)
Battlefield Earth by L. Ron Hubbard (Alien Invasion)