What are the limits of a contract offeror's ability to designate actions that accept the offer?

Question

If I offer a contract, what can I designate as constituting acceptance?

As intuition pumps, here is a collection of increasingly dubious contract offers:

You agree to pay me $1.00 for a peppercorn, due upon delivery.

1. To accept, comment on this question with "I accept and promise to pay $1.00 upon delivery of a peppercorn.".
2. To accept, comment on this question with just the word "peppercorn".
3. To accept, comment on this question with "I would like a peppercorn but I refuse to pay for it.".
4. To accept, comment on this question, questioning its value as a submission to Law Stack Exchange.
5. To accept, comment on this other question with just the word "peppercorn.".

Which of these actually work? Which of these are you still able to do just to thumb your nose at me, despite my having designated them as constituting acceptance, without having to worry about being compelled to pay for an overpriced peppercorn?

Answer 1

There is no bright line rule

There is no bright line rule, but the conduct argued to be acceptance must be interpreted in the context of what the offeror has designated would constitute acceptance. It also must indicate to a reasonable observer that the act was taken "with a view to acceptance of the offer, and not from some other motive or for some other reason; and (b) that it was intended to be acceptance of the offer in question."

So, there are no limits on what the offeror can designate to be acceptance (other than the limits of illegality). But, whether doing the designated act would be understood by a reasonable observer to be a manifestation of acceptance, depends on all the circumstances, including what other reasons the person may have reasonably been understood to have for doing the act.

The offeror is "master of the offer" including the manner in which the contract may be accepted. Where the offeror specifies that acceptance may be by specific conduct, the question becomes "whether the offeror, acting reasonably, would understand that the offeree was assenting to the terms proposed." This is acceptance by conduct. Whether it has occurred is an objective inquiry focusing on how the actions would be understood to a reasonable observer, not an inquiry into the actual states of mind of the offeror or offeree.

It is a question of fact, on a consideration of all the circumstances, whether the conduct of the offeree constitutes an acceptance of the offer. It is open to the offeror to specify the manner in which the offer is to be accepted. Where the offeror does so, this is a significant factor to be taken into account in determining whether or not the conduct of the offeree constitutes acceptance. The conduct of the offeree must be considered in the light of the acceptance provisions specified in the offer.

(Hill v. Develcon Electronics Ltd. (No. 1), 1991 CanLII 7744 (SK KB))

As is the case where acceptance is intended to be, or is appropriately indicated by some statement by the offeree, whether oral or in writing, the nature of acceptance by conduct depends upon the requirements, if any, stipulated by the offeror. ... Yet such conduct must indicate: (a) that the act in question was performed with a view to acceptance of the offer, and not from some other motive or for some other reason; and (b) that it was intended to be acceptance of the offer in question. In such cases the question is whether a reasonable man would interpret the offeree’s conduct as an acceptance of the offer.

(Fridman, The Law of Contract in Canada, 4th ed. (1995), p. 56)

How the above law would apply to any of the circumstances you describe is for a finder of fact, and you are as well placed as any of us to go through that exercise.