THOMSON REUTERS CORP /CAN/ — Major Shareholding Notification 2004

Feb 12, 2004

SC 13G/A 1 a2128771zsc13ga.htm SC 13G/A QuickLinks -- Click here to rapidly navigate through this document User-specified TAGGED TABLE

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 13G/A Under the Securities Exchange Act of 1934 (Amendment No. 2)*

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THE THOMSON CORPORATION
(Name of Issuer)
Common Shares
(Title of Class of Securities)
884903 10 5
(CUSIP Number)

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Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

o Rule 13d-1(b)

o Rule 13d-1(c)

ý Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

ZEQ.=1,SEQ=1,EFW="2128771",CP="KENNETH THOMSON",DN="1",CHK=885777,FOLIO='blank',FILE='DISK018:[04NYC0.04NYC2380]BA2380A.;7',USER='OALBERT',CD='12-FEB-2004;11:25' User-specified TAGGED TABLE

CUSIP No. 884903 10 5 13G/A Page 2 of 6 Pages

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1	Names of Reporting Persons I.R.S. Identification Nos. of above persons (entities only)
	Kenneth R. Thomson
2	Check the Appropriate Box if a member	(a)	o
	of a Group	(b)	ý
3	SEC Use Only
4	Citizenship or Place of Organization
	Canadian
Number of Shares Beneficially Owned by Each Reporting Person With		5	Sole Voting Power
			449,267,429
		6	Shared Voting Power
			0
		7	Sole Dispositive Power
			449,267,429
		8	Shared Dispositive Power
			0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON Aggregate Amount Beneficially Owned by Each Reporting Person
	449,267,429
10	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) o
11	Percent of Class Represented by Amount in Row 9
	68.6%
12	Type of Reporting Person (See Instructions)
	IN

end of user-specified TAGGED TABLE ZEQ.=2,SEQ=2,EFW="2128771",CP="KENNETH THOMSON",DN="1",CHK=386891,FOLIO='blank',FILE='DISK018:[04NYC0.04NYC2380]BA2380A.;7',USER='OALBERT',CD='12-FEB-2004;11:25' THIS IS THE END OF A COMPOSITION COMPONENT

Page 3 of 6 Pages

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Item 1(a).	Name of Issuer:
	The Thomson Corporation
Item 1(b).	Address of Issuer's Principal Executive Offices:
	Metro Center One Station Place Stamford, Connecticut 06902
Item 2(a).	Name of Person Filing:
	Kenneth R. Thomson
Item 2(b).	Address of Principal Business Office or, if None, Residence:
	65 Queen Street West 24 th Floor Toronto, Ontario M5H 2M8, Canada
Item 2(c).	Citizenship:
	Canadian
Item 2(d).	Title of Class of Securities:
	Common Shares
Item 2(e).	CUSIP Number:
	Common Shares: 884903 10 5
Item 3.	If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b), check whether the person filing is a:
	Not applicable.

end of user-specified TAGGED TABLE ZEQ.=1,SEQ=3,EFW="2128771",CP="KENNETH THOMSON",DN="1",CHK=929339,FOLIO='blank',FILE='DISK018:[04NYC0.04NYC2380]JA2380A.;3',USER='SMENEZE',CD='12-FEB-2004;11:02'

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Item 4.	Ownership.
	(a) Amount Beneficially Owned:
	449,267,429
	(b) Percent of Class:
	68.6%
	(c) Number of shares as to which such person has:
	(i)	sole power to vote or to direct the vote:
		449,267,429
	(ii)	shared power to vote or to direct the vote:
		0
	(iii)	sole power to dispose or to direct the disposition of:
		449,267,429
	(iv)	shared power to dispose or to direct the disposition of:
		0
	The 449,267,429 common shares reported as beneficially owned by Mr. Thomson are beneficially owned by Mr. Thomson through intermediate holding companies. Mr. Thomson owns, directly or indirectly, the majority
of the outstanding voting securities of each such intermediate holding company.
Item 5.	Ownership of Five Percent or Less of a Class:
	Not applicable.
Item 6.	Ownership of More than Five Percent on Behalf of Another Person:
	The 449,267,429 common shares reported as beneficially owned by Mr. Thomson are beneficially owned by Mr. Thomson through intermediate holding companies. Mr. Thomson owns, directly or indirectly, the majority
of the outstanding voting securities of each such intermediate holding company.

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Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person:
	Not applicable.
Item 8.	Identification and Classification of Members of the Group:
	Not applicable.
Item 9.	Notice of Dissolution of Group:
	Not applicable.
Item 10.	Certification:
	Not applicable. This statement is not being filed pursuant to Rule 13d-1(b) or Rule 13d-1(c).

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

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February 12, 2004
/s/ KENNETH R. THOMSON Kenneth R. Thomson

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