5.551
Our fundamental principle is that every question which can be decided at all by logic can be decided without further trouble.
(And if we get into a situation where we need to answer such a problem by looking at the world, this shows that we are on a fundamentally wrong track.)
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In 5.551 and 5.552 he maintains that the logical system expounded by the Tractatus ought to be functionally self-contained and self-evident, and efficiently so. Then, in 5.557 he frames this logical system in relation to its “application” in our world, saying that the system should be in contact with its application (see earlier passages about how the picture has “feelers” which connect it to what it depicts), yet without overlapping with it.
