Knowledge without the scientific method
Human beings have secured some kinds of knowledge without using the scientific method.
Can you think of any examples beyond what I've thought of? Are there any of these that you think aren't true knowledge?
1. Mathematical knowledge
Mathematicians may employ a kind of scientific method - e.g. manually computing the elements of a sequence to see whether a given conjecture is experimentally true. But usually the mathematician will go back and try to prove the result with deduction. Experimentally, it seems the basics of mathematics - starting with subitizing, i.e. counting small numbers - appears to be inwrought in the infant mind and the minds of some animals.
I don't know anyone who has really disputed the basic logic employed by the human mind. Even non-Boolean logics are basically a mathematical toy, sometimes for quantum theorists, but the meta-logic remains Boolean logic. The faculty of logic also seems to be inwrought in the human mind.
3. Austrian Economics
The Austrian school of Economics has historically varied in status between being orthodox and heterodox. It is a verbally and argumentatively deduced body of knowledge comprising praxeology or the science of human action, based on the axiom "humans act purposively", and catallactics, which involves additional axioms (such as an empirical one, "humans value leisure" allowing the study of human action in market conditions. The action axiom is taken to be an a priori, apodictic truth, and anyone trying to dispute it is merely providing additional evidence of the axiom's truth. One of the many interesting results of this school is the "economic calculation problem" where von Mises showed in the 1920's that there was no means for a socialist government to rationally organize production of heterogeneous consumption and capital goods in the absence of a market price system enabling the calculation of profits and losses.
It is arguable that propositions like this one are tautological and unfalsifiable: that the fittest genes are aided in their propogation by natural selection.
Geology invokes many a priori rules of thumb such as the law of superposition, the cross-cutting relationships, law of included fragments, principle of original horizontality, principle of lateral continuity, and the principle of faunal succession.
A lot of stuff here, like anthropogenic global warming, is pretty much unfalsifiable, unless you have two copies of Earth to run experiments on and you have a lifespan of hundreds of years. (And personally I think this field is wholly corrupted by Big Government money and statist ideology and I don't believe its results.)