That the truth of one proposition follows from the truth of other propositions, we perceive from the structure of the propositions.
5.131 (1) If the truth of one proposition follows from the truth of others, this expresses itself in relations in which the forms of these propositions stand to one another, and we do not need to put them in these relations first by connecting them with one another in a proposition; for these relations are internal, and exist as soon as, and by the very fact that, the propositions exist.
5.132 If p follows from q, I can conclude from q to p; infer p from q.
The method of inference is to be understood from the two propositions alone.
Only they themselves can justify the inference.
"Laws of inference", which - as in Frege and Russell - are to justify the conclusions, are senseless and would be superfluous.
5.133 All inference takes place a priori.
5.134 From an elementary proposition no other can be inferred.
5.135 In no way can an inference be made from the existence of one state of affairs to the existence of another entirely different from it.
5.136 (3) There is no causal nexus which justifies such an inference.