Now that you are already familiar with the notion of type, individual and instantiation, let’s go through a fundamental ontological meta-property of types - rigidity. To start, let’s take a look at the following pictures:

Dog phases

They show a dog’s development through the years (let’s call him Rex for now). In the first frame (and maybe also in the second) Rex is a Puppy. In the third one he is not a Puppy anymore, but an Adult. However, in all three frames Rex is a Dog and a French Bulldog. Let’s focus on the types Dog and French Bulldog. Can you imagine any other point in time, besides the three shown in the pictures, in which Rex ceased to be either a Dog or a Bulldog? I guess not. Let’s expand our imagination a little. Can you imagine any individual that used to be a Dog but is not anymore? I bet the answer is also no.

If an individual must instantiate a given type in all possible scenarios in which the individual exists, we call that type RIGID. In other words, rigid types are the ones who define essential characteristics to their instances. Other examples of rigid types are: Person, Car, Band, Apple, Country and Company. List of rigid stereotypes: «Category», «Collective», «Kind», «Mode», «Quality», «Quantity», «Relator», and «Subkind».

Rigid examples

Now, let’s focus solely on the type Puppy. By looking at the pictures, we can see that Rex used to be a puppy, but stopped being one after he grew older. Just like Rex, every other dog was once a puppy or will cease to be one someday. If every individual that instantiate a given type in a particular time can cease to do so and still exists, then we call that type ANTI-RIGID. Examples of anti-rigid types are: Student, Employee, Spouse, Elder, Living Person and Healthy Person. List of anti-rigid stereotypes: «Role», «Phase» and «RoleMixin»

AntiRigid examples