Thank you for the thoughtful question. At the heart of critical thinking is inquiry into how we know what we know and making judgments based on reasoning and evidence. Let me expand on this further:

The quintessential question that underlies critical thinking is “How do I know?” Asking how and why we have come to certain beliefs, conclusions or positions is fundamental to a critical approach. It requires reflecting on the origins of ideas and assessing the strength of supporting information rather than passively accepting claims at face value.

Critical thinkers investigate the sources of facts, arguments and opinions. They consider the context, possible biases and reasoned justifications provided rather than simply viewing statements in isolation. Asking “How do I know?” forces examination of evidential foundations and logical coherency. It allows movement beyond initial reactions or feelings to deeper understanding and judgment.

When we ask “How do I know?”, it pushes analysis of both our own and others’ perspectives. All viewpoints should be open to inquiry and critique. By questioning the bases of knowledge, we aim to move past presuppositions, rhetoric and unexamined assumptions. The “how” and “why” prompt acknowledgement of gaps, weaknesses and need for justification rather than assertions alone.

The question “How do I know?” also stimulates consideration of differing viewpoints, contextual factors and alternative interpretations. It encourages searching for additional perspectives and information as a remedy to narrow or limited frameworks of analysis. Exposing ideas to scrutiny and looking for rebuttals or counterevidence helps neutralize biases to arrive at more objective and defendable positions.

Asking how we know further fosters metacognition or thinking about thinking. It requires reflecting on cognitive and affective influences on our reasoning such as preferences, experiences, emotional reactivity and motivation. Self-examination illuminates unrecognized influences that may distort our ability to think in a balanced, open-minded manner. The ability to perceive the invisible influences that shape our thought is pivotal to critical thinking.

“How do I know?” promotes intellectual humility by acknowledging legitimate uncertainty. Not all issues permit completely certain or proven resolutions given human fallibility and complexity of many topics. The question thus supports provisional or probabilistic rather than definitive conclusions. It also recognizes multiple perspectives may have meritworthy components requiring integration rather than outright dismissal.

The quintessential question behind critical thinking is an inquiry into the evidential foundations and logical strengths of the ways we have come to understand issues, form beliefs and arrive at positions. By pushing analysis of how and why we know what we know, it serves to challenge unexamined assumptions, broaden perspectives, enhance objectivity and arrive at more well-supported and defensible viewpoints. At its heart, critical thinking entails careful judgment of knowledge claims and reasoned refutation or confirmation of their validity.