This section is from the book "Handbook Of The Law Of Contracts", by Wm. L. Clark, Jr.. Also available from Amazon: Handbook of the law of contracts.
(1) Contracts in partial restraint of trade, though under seal, require consideration.
40 Leake, Cont 79.
41 Leake, Cont. 79; Powell v. Duff, 3 Camp. 181; Weeks v. Maillardet, 14 East, 508. Blank for sum of money afterwards filled in. Hudson v. Revett, 6 Bing. 368. Since authority to execute a deed must be conferred by instrument under seal, in strictness authority to fill a blank in a deed otherwise executed cannot be conferred by parol. Many courts, however, to-day recognize the validity of a deed in which blanks have been so filled by an agent authorized by parol. See Tiff. Ag. 23. See "Deeds," Dec. Dig. (Key-So.) | 82; Cent. Dig. § 64.
(2) Where there was a consideration, it may be shown to have been illegal or immoral.
(3) Courts of equity will not specifically enforce a deed without consideration.
(4) By statute in some states the distinction between sealed and unsealed instruments is abolished, while in others a seal is merely declared presumptive, but rebuttable, evidence of a consideration.
 
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