EXHIBIT 5.1

                                [Letterhead of]

                            CRAVATH, SWAINE & MOORE
                               [New York Office]

                                                                  April 11, 1997



                          Dean Witter, Discover & Co.
                          ---------------------------
                     Merger with Morgan Stanley Group Inc.
                     -------------------------------------

Dear Ladies and Gentlemen:

     We have acted as counsel for Dean Witter, Discover & Co., a Delaware
corporation ("Dean Witter Discover"), in connection with the Agreement and Plan
of Merger dated as of February 4, 1997, as amended and restated on April 10,
1997 (as amended and restated, the "Merger Agreement"), between Dean Witter
Discover and Morgan Stanley Group Inc., a Delaware corporation ("Morgan
Stanley").  The Merger Agreement provides for, among other things, the merger of
Morgan Stanley with and into Dean Witter Discover (the "Merger").  Dean Witter
Discover will be the surviving corporation in the Merger (the "Surviving
Corporation") and will be renamed Morgan Stanley, Dean Witter, Discover & Co.
Pursuant to the Merger Agreement, each outstanding share of common stock, par
value $1.00 per share, of Morgan Stanley ("Morgan Stanley Common Stock") (other
than certain shares of Morgan Stanley Common Stock owned by Dean Witter Discover
or Morgan Stanley, which will be cancelled) will be converted, upon the
effectiveness of the Merger (the "Effective Time"), into 1.65 shares of common
stock, par value $0.01 per share, of Dean Witter Discover ("Dean Witter Discover
Common Stock").  In addition, pursuant to the Merger Agreement, each outstanding
share of preferred stock, without par value, of Morgan Stanley ("Morgan Stanley
Preferred Stock") (other than certain shares of Morgan Stanley Preferred Stock
owned by Dean Witter Discover or Morgan Stanley, which will be cancelled) will
be converted, at the Effective Time, into one share of a corresponding series of
preferred stock, par value $0.01 per share, of Dean Witter Discover ("Dean
Witter Discover Preferred Stock").  The shares of Dean Witter Discover Common
Stock and Dean Witter Preferred Stock that are to be issued at the 

 
Effective Time in connection with the Merger are referred to herein as the
"Shares".

     We have examined such corporate records, certificates and other documents
as we have considered necessary or appropriate for the purposes of this opinion.
In such examination, we have assumed the genuineness of all signatures and the
authenticity of all documents submitted to us as originals and the conformity to
originals of all documents submitted to us as copies.  We have relied upon the
opinion of Richards, Layton & Finger, Delaware counsel to Dean Witter Discover
as to the due authorization of the Shares.  We have also relied, to the extent
that we deemed such reliance proper, upon certificates of public officials with
respect to the accuracy of material factual matters contained therein which were
not independently established.

     Based on such examination, we are of opinion that the Shares, when issued
at the Effective Time in accordance with the Merger Agreement, will be legally
issued, fully paid and nonassessable.

     We hereby consent to the inclusion of this opinion as an exhibit to the
registration statement on Form S-4 filed with the Securities and Exchange
Commission with respect to the Merger and the issuance of the Shares in
connection therewith and consent to the reference to this opinion under the
heading "Legal Matters" in the Joint Proxy Statement/Prospectus included
therein.


                                                     Very truly yours,

                                                     /s/ Cravath, Swaine & Moore


Dean Witter, Discover & Co.
        Two World Trade Center
            New York, New York 10048

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