Good definitions tend to be essential in helping issues be understood better. Part of what I do, as a transgender girl, is to identify and ponder the various definitions surrounding transgender issues. As a rule, I’ve observed that folks who are not that focused on transgender issues tend to not give them as much thought, and their concepts tend to also not be as precisely defined.
As to what makes a definition better or worse, Aristotle’s approach is fundamental to how I think about this (and much of everything else). In reality, contradictions don’t exist. (Paradoxes, i.e., seeming contradictions abound, like the bent-looking-pencil-in-a-glass-of-water example — I’m talking about true contradictions where something does and doesn’t have the same attribute at the same time and in the same respect). So, arriving at a contradiction in one’s thinking means that one’s thoughts no longer reconcile to reality, i.e., are no longer true, and that a departure from logical thinking has been made.
That’s how I tend to evaluate definitions. I explore their implications and see if they lead to contradictions or not.
The concept of “trans” has been referred to, including by at least one well-meaning person, to be based on “transition” e.g., the person found out that she’s brain-wise a girl and so she changes her looks and style to be that of a girl. By that standard, someone isn’t transgender until she starts changing. I find that definition to fall short since it fails to provide a way to describe what the person has been in the preceding x years or decades of her life.
The concept of “trans” being short for “transgender” as a lifelong condition has no such problem, and if “trans” generically is used as a prefix to imply “beyond” e.g., “trans-atlantic” means beyond the Atlantic ocean, then someone whose gender attributes go beyond the gender-dividing line would be transgender.
If the issues pertain narrowly to the sexual male-female aspect, the person would also be transsexual. On the premise that sexual classification is a subset of the wider concept “gender” then by implication, all transsexual folks are transgender but not all transgender folks are transsexual. Transgender folks might include, for example, intersexed or androgynous people.
In my experience, these more-precise definitions tend to empower my thoughts and conversations to be much more productive.