Antonio Damasio opens by directly challenging the long-standing philosophical assumption (traced to Descartes' mind-body separation) that emotion is fundamentally opposed to rational decision-making, presenting neurological evidence that emotion is actually necessary for effective reasoning.

Why this challenge to conventional assumption matters:

• The traditional view treats emotion as something rational decision-making must overcome or suppress to function properly
• Damasio's clinical neurological case studies instead show that damage to emotional processing centers actually impairs rational decision-making, not improves it
• This finding fundamentally reframes the relationship between emotion and reason as complementary rather than opposed

This opening establishes the book's central, field-shaping thesis, directly challenging centuries of philosophical assumption with specific neurological evidence.