Sri Aurobindo
Letters of Sri Aurobindo
Volume I - Part 4
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I suppose we cannot go so far as to deny that there is such a thing as superstition – a fixed blind belief
without any ground in something that is quite unsound and does not hang together. The human mind readily claps on such beliefs to things which can be or are in themselves true, and this is a mixture which very badly confuses the search for knowledge. But precisely because of that
mixture, because somewhere behind the superstition or not far off from it there is very usually some real truth, one ought to be cautious in using the word or sweeping away with it as a 
convenient broom the true, the partly true and the unfounded together and claiming that the bare ground left is the only truth of the matter.
Current publication:
Sri Aurobindo. Letters on Yoga. I // CWSA.- Volume 28. (≈ 22 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2012.- 590 p.
Other publications:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
[Largest or earliest found passage: ] Sri Aurobindo. Letters of Sri Aurobindo: In 4 Series.- First Series [On Yoga].- Bombay: Sri Aurobindo Sircle, 1947.- 416 p.