Exhibit 5 and 23.1

              [Letterhead of Fair, Isaac and Company, Incorporated]

                                   -----, ----


Fair, Isaac and Company, Incorporated
200 Smith Ranch Road
San Rafael, CA  94903

Re:  Registration Statement on Form S-8

Ladies and Gentlemen:

With  reference to the  Registration  Statement on Form S-8 to be filed by Fair,
Isaac and Company,  Incorporated,  a Delaware corporation (the "Company"),  with
the  Securities  and Exchange  Commission  under the  Securities Act of 1933, as
amended,  relating to  the 1,500,000  shares of the Company's  common stock, par
value $0.01 per share (the "Common Stock"), issuable pursuant to the Fair, Isaac
and Company,  Incorporated 1999 Employee Stock Purchase Plan (the "Plan"), it is
my opinion that such shares of the Common Stock of the Company,  when issued and
sold in  accordance  with the  Plan,  will be  legally  issued,  fully  paid and
nonassessable.

I hereby  consent to the filing of this opinion with the Securities and Exchange
Commission as Exhibit 5.1 to the Registration Statement.

                                         Very truly yours,

                                         /s/ Peter L. McCorkell, Esq.

                                         Peter L. McCorkell, Esq.
                                         Executive Vice President, Secretary,
                                         and General Counsel
                                         Fair, Isaac and Company, Incorporated


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