5.1311 When we infer q from p C q and Pp, the relation between the
propositional forms of 'p C q' and 'Pp' is masked, in this case, by our
mode of signifying. But if instead of 'p C q' we write, for example, 'p|q .
| . p|q', and instead of 'Pp', 'p|p' (p|q = neither p nor q), then the
inner connexion becomes obvious. (The possibility of inference from (x) .
fx to fa shows that the symbol (x) . fx itself has generality in it.)


5.132 If p follows from q, I can make an inference from q to p, deduce p
from q. The nature of the inference can be gathered only from the two
propositions. They themselves are the only possible justification of the
inference. 'Laws of inference', which are supposed to justify inferences,
as in the works of Frege and Russell, have no sense, and would be
superfluous.


5.133 All deductions are made a priori.


5.134 One elementary proposition cannot be deduced form another.


5.135 There is no possible way of making an inference form the existence of
one situation to the existence of another, entirely different situation.


5.136 There is no causal nexus to justify such an inference.