There are four basic tastes

What actually happened

Kikunae Ikeda identified umami in 1908 while working out why kombu broth tasted savory in a way the four tastes did not explain. He isolated glutamate as the compound responsible. Western science largely ignored him for most of a century, partly because his paper was in Japanese and partly because monosodium glutamate acquired a bad reputation for unrelated reasons.

The argument ended when receptors were found. In 2000 researchers identified a taste receptor responding specifically to glutamate, giving umami the same physiological standing as the other four. Research since has built a solid case for oleogustus, a distinct taste for fatty acids, and there are ongoing candidates for others. If your textbook's taste chapter had four items, it was already ninety years behind Ikeda when it was printed.