How many basic forces are now taken to account for all known phenomena?

1. Physics has repeatedly unified apparently separate forces. 2. The development of special relativity and empirical observations at atomic scales pushed that programme further. 3. They led to the idea that there are four basic forces that account for all known phenomena. 4. These forces are called fundamental. 5. Gravity, electromagnetism and the two nuclear forces make up that set of four. _Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 4 'Dynamics: Force and Newton's Laws of Motion', sections 4.1-4.8_