What is the antonym of solipsism?

There isn't one single perfect antonym for solipsism. This is because solipsism is a very specific philosophical idea, and its opposite could be considered from various angles. Here are a few possibilities depending on the context:

1. Realism: This is the most general and direct antonym. Realism asserts that the external world exists independently of our minds.

2. Altruism: This focuses on the opposite of solipsism's self-centeredness. Altruism emphasizes concern for others and their well-being.

3. Empiricism: This highlights the reliance on sensory experience as evidence for the external world, which solipsism denies.

4. Sociality: This emphasizes the interconnectedness of human beings and the importance of social interactions, which solipsism dismisses.

5. Objectivity: This focuses on the existence of a reality independent of individual perception, which solipsism denies.

The best antonym depends on the specific aspect of solipsism you want to contrast.