 I'm not going to go through all of this again because I'm already over time for this video, but it's really important that you have some comparison point and we'll have a look in a bit more detail at exactly why these ideas change. But in science, we are often wrong. That is one of the great things about science. Science isn't worried about being wrong, but science is about empirical evidence that suggests where that wrongness is and allows us to develop and refine our theories in order to ensure that all of the observations that we make fit our theories or models. We don't change the facts, we change our ideas. We reconstruct our models, or we improve on our models. We look at where those limitations are and why perhaps a certain definition or a certain model or a certain idea about what we think about a certain thing such as an acid or a base may change as we gather more data, more information, carry out more experiments. This is a really important thing when you're doing experiments yourself to think about what's going on in each of these experiments that you're looking at and why our definitions and why our ideas, particularly our models, can change over time. I've put here just a comparison between the acid and base definitions for the Arrhenius definition, the Brunster-Laurid definition and the Lewis definition. I've left out both Davey and also Lavoisier from this table, which you can include them if you want to do that as well. Setting out work in a comparison table like this is also a very good way of not only studying but also of representing answers in examinations, and they're things that are very important techniques that we'll talk about to you as we continue through this course. Thanks for watching.