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                                                                     EXHIBIT 5.1

                                  [Letterhead]


                                December 11, 1997

Synopsys, Inc.
700 East Middlefield Road
Mountain View, CA  94043

            RE:  REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

            We have examined the Registration Statement on Form S-8 to be filed
by you with the Securities and Exchange Commission on or about December 11, 1997
(the "Registration Statement"), in connection with the registration under the
Securities Act of 1933, as amended, of an aggregate of 2,671,864 shares of your
Common Stock, par value $0.01 per share, (the "Shares") to be issued pursuant to
the Viewlogic Systems, Inc. 1991 Restated Stock Option Plan, as amended, the
Viewlogic Systems, Inc. 1991 Outside Directors' Stock Option Plan, and the
Viewlogic Systems, Inc. 1996 Outside Directors' Stock Option Plan (collectively,
the "Plans"). As your counsel in connection with this transaction, we have
examined the proceedings taken and are familiar with the proceedings proposed to
be taken by you in connection with the issuance and sale of the Shares pursuant
to the Plans.

            It is our opinion that, when issued and sold in the manner described
in the Plans and pursuant to the agreements which accompany each grant under the
Plans, the Shares will be legally and validly issued, fully paid and
non-assessable.

            We consent to the use of this opinion as an exhibit to the
Registration Statement, and further consent to the use of our name wherever
appearing in the Registration Statement and any amendments thereto.

                                          Sincerely,

                                          WILSON SONSINI GOODRICH & ROSATI
                                          Professional Corporation

                                          /s/ Wilson Sonsini Goodrich & Rosati