[LETTERHEAD OF COOLEY GODWARD LLP] 

                                                                   Exhibit 5.1

September 4, 1998

Aspect Development, Inc.
1300 Charleston Road
Mountain View, CA 94043                            PRIVILEGED AND CONFIDENTIAL
                                                         ATTORNEY WORK PRODUCT

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection 
with the filing by Aspect Development, Inc. (the "Company") of a Registration 
Statement on Form S-8 (the "Registration Statement") with the Securities and 
Exchange Commission covering the offering of up to 2,200,000 shares of the 
Company's Common Stock, $.001 par value, (the "Shares") pursuant to its 1992 
Stock Option Plan ("the Plan").

In connection with this opinion, we have examined the Registration Statement 
and related Prospectus, your Certificate of Incorporation and By-laws, as 
amended, and such other documents, records, certificates, memoranda and other 
instruments as we deem necessary as a basis for this opinion. We have assumed 
the genuineness and authenticity of all documents submitted to us as 
originals, the conformity to originals of all documents submitted to us as 
copies thereof, and the due execution and delivery of all documents where due 
execution and delivery are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion 
that the Shares, when sold and issued in accordance with the Plan, the 
Registration Statement and related Prospectus, will be validly issued, fully 
paid, and nonassessable (except as to shares issued pursuant to certain 
deferred payment arrangements, which will be fully paid and nonassessable when
such deferred payments are made in full.)

We consent to the filing of this opinion as an exhibit to the Registration 
Statement.

Very truly yours,

COOLEY GODWARD LLP

By:
     /s/ Andrea Vachss
     ---------------------
      Andrea Vachss, Esq.