In the next piece of text taken from the article 'Only possible critique of the atomistic concepts' by Rudolf Steiner, the principle of knowledge based on experience is formulated once again in very clear sentences. In this article of the still very young Steiner the wonderful musicality of the composition is already there. He preludes on the first theme - which is this reversal of the relationship of sensual perception and concepts, stating that the sensual world is another form of the conceptual world, that the latter actually is the basis and that the former is one of its forms, which is necessary to have though - and comes then to a repetition of the preluding tones into a first grand playing of the theme, which brings the relief of full comprehension.
Rudolf Steiner, next paragraph of the article:
'From this, one sees at the same time how unfruitful the undertaking would be to want to make out anything about the outer world without the help of perception. How can one gain possession of the concept in the form of viewing, without accomplishing the viewing itself? Only when one sees that what perception offers is concept and idea, but in an essentially other form than in pure thinking's form freed of all empirical content, and that this form is what makes the difference, does one comprehend that one must take the path of experience.
But if one assumes the content to be what matters, then nothing can be put forth against the assertion that the same content could after all also be acquired in a manner independent of all experience. So experience must indeed be the maxim of the philosophy of nature, but at the same time, recognition of the concept in the form of outer experience.
And here is where modern natural science, by seeking no clear concept of experience, got on the wrong track. In this point it has been attacked repeatedly, and is also easily open to attack. Instead of acknowledging the apriority of the concept, and taking the sense world as but another form of the same, it regards the same as a mere derivative of the outer world, which for it is an absolute Prior. The mere form of something is thus stamped the thing itself.
Atomism, to the extent that it is materialistic, issues from this unclearness of the concepts. We want here, based on the preceding, to subject it to a careful, and — as I believe I can assume — the only possible, critique.’ (Italics by MM)