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Exhibit 31.2

# CERTIFICATION

I, Tom Manley, Senior Vice President,
Finance & Administration and Chief Financial Officer (Principal Financial Officer and
Chief Accounting Officer), certify that:

|1. | I have reviewed this report on Form 10-Q of Cognos Incorporated;
|-- | ----------------------------------------------------------------

|2. | Based on my knowledge, this report does not contain any untrue statement of a
          material fact or omit to state a material fact necessary to make the statements
          made, in light of the circumstances under which such statements were made, not
          misleading with respect to the period covered by this report;
|-- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|3. | Based on my knowledge, the financial statements, and other financial information
          included in this report, fairly present in all material respects the financial
          condition, results of operations and cash flows of the registrant as of, and
          for, the periods presented in this report;
|-- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|4. | The registrants other certifying officer and I are responsible for
          establishing and maintaining disclosure controls and procedures (as defined in
          Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:
|-- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|a) |  | Designed
such disclosure controls and procedures, or caused such disclosure           controls and
procedures to be designed under our supervision, to ensure that           material
information relating to the registrant, including its consolidated
          subsidiaries, is made known to us by others within those entities, particularly
          during the period in which this report is being prepared;
|-- |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|b) |  | [Paragraph
omitted pursuant to SEC Release Nos. 33-8238 and 34-47986];
|-- |  | ----------------------------------------------------------------------

|c) |  | Evaluated
the effectiveness of the registrants disclosure controls and           procedures
and presented in this report our conclusions about the effectiveness           of the
disclosure controls and procedures, as of the end of the period covered           by this
report based on such evaluation; and
|-- |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|d) |  | Disclosed
in this report any change in the registrants internal control           over
financial reporting that occurred during the registrants most recent
          fiscal quarter that has materially affected, or is reasonably likely to
          materially affect, the registrants internal control over financial
          reporting; and
|-- |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|5. | The registrants other certifying officer and I have disclosed, based on
          our most recent evaluation of internal control over financial reporting, to the
          registrants auditors and the audit committee of the registrants
          board of directors (or persons performing the equivalent functions):
|-- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|a) |  | All
significant deficiencies and material weaknesses in the design or operation           of
internal control over financial reporting which are reasonably likely to
          adversely affect the registrants ability to record, process, summarize
and           report financial information; and
|-- |  | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|b) |  | Any
fraud, whether or not material, that involves management or other employees           who
have a significant role in the registrants internal control over
          financial reporting.
|-- |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|October 1, 2004
___________________________________________________ |  | /s/ Tom Manley
___________________________________________________
|------------------------------------------------------------------- |  | ------------------------------------------------------------------
|Date                                                                |  | Tom Manley                                                        
|                                                                    |  | Senior Vice President, Finance and Administration                 
|                                                                    |  | and Chief Financial Officer                                       
|                                                                    |  | (Principal Financial Officer and Chief Accounting Officer)        

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