Tendency and Propensity

Tendency

When you have a tendency to act a certain way, it means you are inclined to do it. Therefore, the word tendency is a synonym for inclination and proneness.
Ex: Sarah is a sweet girl, but she has a tendency to talk too much. That's why I never invite her to the cinema because she can't keep quiet long enough for me to enjoy the film.
Ex: I just love visiting my family, but they have a tendency to tell me what to do. So, I only stay long enough to enjoy their company and go back home when things get uncomfortable.
If you have a tendency toward a behavior or activity, it is in your nature. When something is in someone's nature, that means it comes easily or natural for them to do.
Ex: Adventure sports like rock climbing or water rafting are in Laura's nature. Even as a little girl, she was always spending time outside and taking on new physical challenges.
Ex: Becoming a nurse is just in my nature. I love taking care of people and have always had a strong interest in what makes the body work.

Propensity

A person's propensity is the likelihood or chance they will behave in a certain way. Therefore, propensity is a synonym for tendency or inclination.
Ex: Carl is very intelligent, but he has a propensity for handing in his homework late. For that reason, he does not get very good marks at school.
Ex: If you have a propensity toward travel, you might want to become a teacher. Teachers can travel all over the world sharing their knowledge with others.
When you have a propensity for something, it might be in your genetic makeup. When you have a genetic makeup for something, it means you are physically conditioned or made to act in that way.
Ex: Many professional athletes were born to be stars. It is in their genetic makeup to be successful in a sport or physical competition.
Ex: Some people have to work hard to graduate from university, while it comes easier to others. Some people just have a genetic makeup that makes it easier for them to learn and study from books.