Well, that’s what all writers do, isn’t it? We get inside the heads of fictional people and other critters, find out their motivations (or give them some) and then see what happens. Right?
But what if you need a character with a mind that works in a very different way from yours?
You look at good historical writing, for starters. And great works by other writers of fiction. As a history professor said, “the past is another country. They do things differently there.” Dr. Art Macavoy added a vital point: “But it’s not a different planet.” Translated into author, people in different times and places think and act for reasons that might be very strange and abhorrent to us, but that make logical sense in their world (most of the time). However, they are still people with similar basic desires and needs.
This applies to non-human species that you create. What is the basic goal of the individual and his culture? What does that person do in order to live up to society’s rules, or to skirt them so he can do what he wants to do? If all Horla are trained from birth that earning money is the highest good, especially if you can persuade or coerce others to do the work for you, legal or not, then everything in Horla culture will focus on that. Social structure (family or clan corporations), social rank, what is considered good and evil, all those need to tie into the basic foundation, unless you the author show that your particular Horla has a really good reason why he does something different.
However, self-preservation is even more powerful. No Horla is going to accept the greatest deal in the history of the galaxy if it means he’s going to die. Unless he thinks he can find fine print and a loophole in the contract. When the shooting starts, he’s going to flee or fight, just like a human.
However, aliens can also do things like we do, but for very different reasons, which changes how an ambassador or businessman would have to work with them. In our world, Chinese families and individuals established businesses that looked, from the outside, like western joint-stock corporations. The shares would pass down family lineages, and the occasional outsider would buy in, others would sell shares, and there would be distributions of profits to share owners. But the goal was to provide income to pay for dowries, funerals, and ancestor rites, and shares could not be sold on a market or traded the way western joint-stock shares were. So people bought shares to augment a dowry, for example, planning to sell when they needed to marry off a daughter.
If the lineage made sufficient money to invest in good farmland or real-estate, then they sold or sometimes closed the business, no matter how much income it was generating at that moment. Why? Because land was more honorable, taxes far less, and provided income that could support a gentleman and bureaucrat, which was the ideal thing to have in the lineage.
In a more personal example, the historian Steven Ozment describes the patrician families of Nuremberg in the 1400s-mid 1500s. One man and his wife had eight children die before age one. Child nine, a boy, lived. The father resisted having the boy named until it appeared that he would live, and then fretted because at age three, the child still preferred milk to wine. The father was terrified that the boy would die from bad milk, and expressed great relief in a letter to a family member when the little boy finally started drinking wine.
Eight children. All dead. Then at last, one survives, and instead of rejoicing, the father holds back for several days to weeks before daring to believe that perhaps this one will live. Fast forward to 1910 and the Texas Hill Country. A neighbor of my grandmother’s family had the crawler baby toddle off the high porch, fall into a slop-barrel, and drown. Gammy was with her father when they went to pay condolences. The “old Dutchman” was on the porch, and Gammy’s father expressed his sorrow and asked about how the family fared. Gammy said, “The old Dutchman pulled on his pipe, then said, ‘Vell, vas too bad, but vas too young to vork.'” Stoic? Cold? Or pragmatic?
But even within a society that sees some members as almost without value, individuals can stick out. Ten years ago or so I read an article about vaccinations and the problems faced after a rumor went out that the polio vaccine caused infertility. The author had a picture of an Afghani man and his daughter. The girl was crippled because of polio. her father had refused the vaccination, and now his child would always suffer. Even though she was “just” a daughter, he loved her and felt horrible for what happened. They traveled with the medical techs, and he told people what had happened and urged them to ignore the rumors and have their children protected.
Now, extrapolate that into a different culture.
I’ve found over the years that reading about the past and past minds helps me get into alien characters more easily. And writing aliens helps me better get inside the minds—as much as we can—of pre-modern and non-western people. Apparently I do this well enough to spook my students on occasion. I’ve been told I do “historical heavies” a little too convincingly. But walking the students through pre-modern logic really helps them understand why Charlemagne or Elizabeth I did things that seem counterproductive to us.
References: Ozment, The Burgermeister’s Daughter, and When Fathers Ruled
Richard van Glahn The Economic History of China