Solipsism (/ˈsɒlɪpsɪzəm/ ( listen); from Latin solus 'alone', and ipse 'self') is the philosophical idea that only one's mind is sure to exist the mind

Solipsism

• Solipsism (/ˈsɒlɪpsɪzəm/ ( listen); from Latin solus 'alone', and ipse 'self') is the philosophical idea that only one's mind is sure to exist.

• the mind can not conclude the existence of anything external, therefore nothing external exists, only the appearance of it.

Scepticism

Skepticism, also spelled scepticism, in Western philosophy, the attitude of doubting knowledge claims set forth in various areas. Skeptics have challenged the adequacy or reliability of these claims by asking what principles they are based upon or what they actually establish.

Agnosticism

Agnosticism, (from Greek agnōstos, “unknowable”), strictly speaking, the doctrine that humans cannot know of the existence of anything beyond the phenomena of their experience.

• Critical thinking is the ability to think clearly and rationally about what to do or what to believe. It includes the ability to engage in reflective and independent thinking

Critical thinking

"Ought implies can" is an ethical formula ascribed to  Immanuel Kant  that claims an agent, if morally obliged to perform a certain action, must logically be able to perform it

"Ought", "can" and "is"