1

                                                                    EXHIBIT 5.01


                                 June 28, 2000



HNC Software Inc.
5935 Cornerstone Court West
San Diego, CA  92121-3728

Gentlemen/Ladies:

        At your request, we have examined the Registration Statement on Form S-8
(the "REGISTRATION STATEMENT") to be filed by you with the Securities and
Exchange Commission (the "COMMISSION") on or about June __, 2000, in connection
with the registration under the Securities Act of 1933, as amended, of an
aggregate of 2,150,000 shares of your Common Stock, $0.001 par value (the
"SHARES"), that are subject to issuance by you upon the exercise of stock
options (collectively, the "OPTIONS") to be granted by you under (a) your 1995
Equity Incentive Plan, as amended (the "INCENTIVE PLAN"); and (b) your 1995
Directors Stock Option Plan, as amended (the "DIRECTORS PLAN"); and the exercise
of stock purchase rights to be granted by you under your 1995 Employee Stock
Purchase Plan, as amended (the "PURCHASE PLAN"). The Incentive Plan, the
Directors Plan and the Purchase Plan are collectively referred to herein as the
"PLANS" and each individually as a "PLAN."

        In rendering this opinion, we have examined the following:

        (1)    your registration statement on Form S-1 (Registration Number
               33-91932) filed with and declared effective by the Commission on
               June 20, 1995, together with the Exhibits filed as a part
               thereof;

        (2)    your registration statement on Form 8-A filed with the Commission
               on May 26, 1995, together with the order of effectiveness issued
               by the Commission therefor on June 20, 1995;

        (3)    the Registration Statement, together with the exhibits filed as a
               part thereof, including without limitation the Incentive Plan,
               the Directors Plan, the Purchase Plan, the forms of stock option
               agreements and stock option exercise agreements used under the
               Incentive Plan and the Directors Plan that are exhibits to the
               Registration Statement (collectively, the "OPTION AGREEMENTS"),
               and the form of Subscription Agreement and Enrollment Form used
               under the Purchase Plan (collectively, the "PURCHASE DOCUMENTS")
               which you have represented to us constitute all the plans and
               agreements that apply to the Options and the Plans;

        (4)    the prospectuses prepared in connection with the Registration
               Statement;

        (5)    the minutes of meetings and actions by written consent of the
               stockholders and Board of Directors that are contained in your
               minute books that are in our possession, specifically including,
               but not limited to, the minutes of the meetings of the Board of
               Directors and the stockholders and all actions taken by the
               written consent of the Board of Directors and/or the stockholders
               which approve all amendments to the Plans;

        (6)    the stock records that you have provided to us (consisting of a
               certificate from your transfer agent of even date herewith
               verifying the number of your issued and outstanding shares of
               capital stock and a list of option and warrant holders respecting
               your capital stock and of any rights to purchase capital stock
               that was prepared by you, verifying the number of such issued and
               outstanding securities);

        (7)    a Management Certificate addressed to us and dated of even date
               herewith executed by you and containing certain representations
               by you to us; and


                                       44
   2

        (8)    your Restated Certificate of Incorporation, as amended and
               Bylaws, as amended, both included as exhibits to the Registration
               Statement.

        In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the genuineness of all signatures on
original documents, the authenticity and completeness of all documents submitted
to us as originals, the conformity to originals and completeness of all
documents submitted to us as copies, the legal capacity of all natural persons
executing the same, the lack of any undisclosed terminations, modifications,
waivers or amendments to any documents reviewed by us and the due execution and
delivery of all documents where due execution and delivery are prerequisites to
the effectiveness thereof.

        As to matters of fact relevant to this opinion, we have relied solely
upon our examination of the documents referred to above and have assumed the
current accuracy and completeness of the information obtained from records
referred to above. We have made no independent investigation or other attempt to
verify the accuracy of any of such information or to determine the existence or
non-existence of any other factual matters; however, we are not aware of any
facts that would cause us to believe that the opinion expressed herein is not
accurate.

        We are admitted to practice law in the State of California, and we
render this opinion only with respect to, and express no opinion herein
concerning the application or effect of the laws of any jurisdiction other than,
the existing laws of the United States of America, of the State of California
and, with respect to the validity of corporate action and the requirements for
the issuance of your stock, of the State of Delaware.

        Based upon the foregoing, it is our opinion that the Shares that may be
issued and sold by you upon the exercise of (a) stock options granted or to be
granted under the Incentive Plan and the Directors Plan; and (b) purchase rights
granted or to be granted under the Purchase Plan, when issued, sold and
delivered in accordance with the applicable Plan and the applicable Option
Agreement or Purchase Document, as applicable, to be entered into thereunder and
in the manner and for the consideration stated in the Registration Statement and
the relevant Prospectus, will be validly issued, fully paid and nonassessable.

        We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Prospectus constituting a part thereof and any
amendments thereto. This opinion speaks only as of its date and we assume no
obligation to update this opinion should circumstances change after the date
hereof. This opinion is intended solely for use in connection with the issuance
and sale of Shares subject to the Registration Statement and is not to be relied
upon for any other purpose.



                               Very truly yours,

                               /s/ FENWICK & WEST LLP

                               FENWICK & WEST LLP


                                       45