Definition: Given the Question and Answer pair, detect whether the answer is acceptable or not. Denote acceptable answer as "yes", otherwise denote as "no". An acceptable answer is consistent with the context in question, detailed, long, and uses general knowledge of English. Answers that are not definite and suggest a variety of options are not acceptable answers.
Input: Question: I'm a non-native English speaker, and my automatic spellchecker seems to accept both therefore and therefor. Is one orthography preferred ? Is that a British vs. American difference ? Or an old vs. more recent orthography ? Or something else ? 
Answer: Therefor means for that. For example: Here we sell guitars and accessories therefor. Therefor is one of a whole series of adverbs: thereof (of that), thereafter(after that), therein (in there), etc. If you are familiar with German - the Germanic sister of English - you can find a direct analogy there: for = fur therefor, for that = dafur (literally, therefor) Therefore, as you must know, means as a (logical) consequence.

yes