Heidegger insists that the hand is not merely an instrument that human beings happen to possess, as animals possess paws or claws. The hand is essentially human: it is through the hand that speech and thought are given form, through the hand that craft is practised, through the hand that the signature commits a person to their word. What the hand touches, it does not merely grasp; it lets things rest in their own being while attending to them. The hand that genuinely handles something is already thinking — already engaged in a bringing-forth that respects the nature of what is brought forth.
Heidegger's observation that the typewriter severs the connection between the hand and the word has become one of the most discussed — and mocked — passages in his work. The point is not luddism: it is that the handwritten word bears the mark of the whole person in a way that mechanically reproduced text does not, and that this difference is philosophically significant rather than merely aesthetic. The degradation of craft — the replacement of genuine handwork by mechanical production — is the social counterpart of the decline of thinking that is his central theme throughout the lectures.
The meditation on the hand appears in Part One, Lecture 5 of What Is Called Thinking? It has attracted both careful analysis and considerable satire. Friedrich Kittler's Discourse Networks 1800/1900 is among the most serious engagements with Heidegger's claim about typewriting and the word.