To learn by example is to submit to authority. ...By watching the master and emulating his efforts in the presence of his example, the apprentice unc… - Michael Polanyi

The recognition of certain basic impossibilities has laid the foundations of some major principles of physics and chemistry; similarly, recognition of the impossibility of understanding living things in terms of physics and chemistry, far from setting limits to our understanding of life, will guide it in the right direction. And even if the demonstration of this impossibility should prove of no great advantage in the pursuit of discovery, such a demonstration would help to draw a truer image of life and man than that given us by the present basic concepts of biology.

In a strict usage the same symbol should never represent the act of sincerely asserting something and the content of what is asserted. For the symbolic distinction between the two, Frege has introduced the 'signpost' symbol. ... <math>\vdash</math> p is to signify the actual assertion of p, while the bare symbol p must henceforth be used only as part of a sentence. ... It should be clear from the modality of a sentence whether it is a question, a command, an invective, a complaint or an allegation of fact.

A declaratory sentence can be asserted, because it is an incomplete symbol, of indeterminate modality; while a question, a command, an invective, or any other sentence of fixed intention can no more be asserted than could my act of hewing wood or of drinking tea.