law: Patents Act, 1970
  25. Opposition to grant of patent
  (1) At any time within four months from the date of
  
  advertisement of the acceptance of a complete specification under this Act (or
  
  within such further period not exceeding one month in the aggregate as the
  
  Controller may allow on application made to him in the prescribed manner before
  
  the expiry of the four months aforesaid) any person interested may give notice
  
  to the Controller of opposition to the grant of the patent on any of the
  
  following grounds, namely,-
  (a) that the applicant for the patent or the
  
  person under or through whom he claims, wrongfully obtained the invention or
  
  any part thereof from him or from a person under or through whom he claims;
  (b) that the invention so far as claimed in
  
  any claim of the complete specification has been published before the priority
  
  date of the claim-
  (i) in any specification filed in pursuance of
  
  an application for a patent made in India on or after the 1st day of January,
  
  1912; or
  (ii) in India or
  
  elsewhere, in any other document:
  PROVIDED  that the ground specified in sub-clause
  
  (ii) shall not be available where such publication does not constitute an
  
  anticipation of the invention by virtue of sub-section (2) or sub-section (3)
  
  of section 29;
  (c) that the invention so far as claimed in
  
  any claim of the complete specification is claimed in a claim of a complete specification
  
  published on or after the priority date of the applicant's claim and filed in
  
  pursuance of an application for a patent in India, being a claim of which the
  
  priority date is earlier than that of the applicant's claim;
  (d) that the invention so far as claimed in
  
  any claim of the complete specification was publicly known or publicly used in
  
  India before the priority date of that claim.
  Explanation:  For the purposes of
  
  this clause, an invention relating to a process for which a patent is claimed
  
  shall be deemed to have been publicly known or publicly used in India before
  
  the priority date of the claim if a product made by that process had already
  
  been imported into India before that date except where such importation has
  
  been for the purpose of reasonable trial or experiment only;
  (e) that the invention so far as claimed in
  
  any claim of the complete specification is obvious and clearly does not involve
  
  any inventive step, having regard to the matter published as mentioned in
  
  clause (b) or having regard to what was used in India before the priority date
  
  of the applicant's claim;
  (f) that the subject of any claim of the
  
  complete specification is not an invention within the meaning of this Act, or
  
  is not patentable under this Act;
  (g) that the complete specification does not
  
  sufficiently and clearly describe the invention or the method by which it is to
  
  be performed;
  (h) that the applicant has failed to disclose
  
  to the Controller the information required by section 8 or has furnished the
  
  information which in any material particular was false to his knowledge;
  (i) that in the case of a convention
  
  application, the application was not made within twelve months from the date of
  
  the first application for protection for the invention made in a convention
  
  country by the applicant or a person from whom he derives title, but on no
  
  other ground.
  (2) Where any such notice of opposition is duly given, the
  
  Controller shall notify the applicant and shall give to the applicant and the
  
  opponent an opportunity to be heard before deciding the case.
  (3) The grant of a patent shall not be refused on the ground
  
  stated in clause (c) of sub-section (1) if no patent has been granted in
  
  pursuance of the application mentioned in that clause; and for the purpose of
  
  any inquiry under clause (d) or clause (e) of that sub-section, no account
  
  shall be taken of any secret use.