What does like cause produce like effects mean?

Answer 1

positive = positive negative = negative i am guessing. if i smile i most likely will get a smile back usually- if i growl at someone or sneer or something i will get a negative effect back

Actually this is (almost) a quote from the empiricist philosopher David Hume, who argued that it is a matter of experience that "like effects imply like causes" or "like causes always produce like effects." Causes and effects can be any events in the Universe that are causally related (e.g. a flame heating a pan of water). He is simply saying that we know the 'law' of cause and effect not through some innate knowledge, but because we constantly observe it to be the case (i.e. flames applied to pans of water always heat the water).

He isn't saying that it is impossible to produce an effect (say, a musical note) in more than one way, but that where two seemingly different causes do produce the same effect (say, a piano and a synthesizer), there must be something that they have in common, and this accounts for the similarity in the effect. And where seemingly similar causes produce differing effects, we should be able to find some difference in the causes that accounts for the different effects.