Poppers demarcation criterion for science

• a theory is scientific if and only if it is in principle falsifiable

False scientific theories also count as scientific theories according to popper

Many theories have been refuted in the history of science

• Biology: Spontaneous generation (of organisms)
• Chemistry: Phlogiston theory
• Cosmology: steady state theory (replaced by big bang theory)

Consequences of this line of thinking:

• Scientific theories must take a risk: be open to refutation!
• Not about the content but formulation: if a theory is too vague, then nothing will falsify it.
  • Examples:
    • Artificial intelligence cannot think. (What do you mean by think?)
    • Mature democracies never start a war (do you assume immature = starting a war?)
    • The criterion is not directly about truth and falsity of theories.

However, sometimes illusions may be beneficial.

Beneficial illusions are unjustified but useful beliefs to the believer

Decision theory: formal/scientific tool to reason about decisions, given what we know (and don’t), and our concerns and preferences (which we quantify).