Why isn&#39;t a simple sales contract unilateral?
<p>Poole, Shaw-Mellors. <a href="https://www.amazon.co.uk/Contract-Law-Concentrate-Jill-Pool/dp/0198840446/ref=dp_ob_title_bk" rel="nofollow noreferrer"><em>Contract Law Concentrate</em> (4 ed 2019)</a>. p 5.</p>

<blockquote>
  <h1>The key distinction: bilateral and unilateral agreements</h1>
  
  <p>Broadly, agreements will be one of two types:
  • bilateral
  • unilateral.</p>
  
  <h2>Definition</h2>
  
  <p><strong>Bilateral agreements:</strong> by far the most common in practice and consist of a promise in
  exchange for a promise. Bilateral means both parties are bound on the exchange of promises,
  although there has yet to be any performance of those promises.<br>
  &nbsp; &nbsp; &nbsp; A typical sale of goods agreement is bilateral.     </p>
  
  <h3>Practical example 1</h3>
  
  <p>Alex offers (or promises) to sell his bicycle to Becky for £150 and Becky accepts, thereby promising
  to pay £150. (We will use this as our example of a bilateral agreement and look at variations and additions
  to the facts throughout this chapter.)</p>
  
  <h2>Definition</h2>
  
  <p><strong>Unilateral agreements:</strong> consist of a promise in exchange for an act. It follows that only one party is
  bound at the outset by a promise. The other’s acceptance is the performance of the requested act.<br>
  &nbsp; &nbsp; &nbsp; For example, a typical unilateral agreement will involve an offer of a reward and may be
  phrased as an ‘if’ contract: I promise to pay £50 to anyone who finds and returns my lost dog.</p>
  
  <h3>Practical example 2</h3>
  
  <p>Daniel offers (or promises) a free watch to anyone who returns three tokens from the packets of
  cereal he manufactures, together with a cheque for £5. Emily accepts by returning the three tokens
  with her cheque for £5. (We will use this as our example of a unilateral agreement and return to this
  example later in the chapter.)</p>
</blockquote>

<p>p 6.</p>

<blockquote>
  <h2>Making the correct distinction.</h2>
  
  <p>It is not possible to accept a unilateral offer by promising to
  find and return the lost dog or by promising to collect and return the tokens and the cheque. By
  comparison, the agreement to sell the bicycle cannot be unilateral. Students sometimes suggest
  that a simple sale contract is unilateral by interpreting the act of paying for the bicycle as the
  requested act. This is incorrect since, as long as it is possible to accept by promising to buy (which
  it is in the example), the agreement will be bilateral.</p>
</blockquote>

<p>I don't fathom what's "incorrect" about "interpreting the act of paying for the bicycle as the
requested act". In the end Alex will require £150 from Becky, not just Becky's promise to pay £150. </p>

<p>I agree Becky promised to buy the bike for £150, but at some point she must pay the £150. She can't just keep promising to buy for £150 without paying the £150! </p>

<h2>You’re confusing the <em>formation</em> of a contract with the <em>execution</em> of it</h2>

<p>The point in time at which a contract is <em>formed</em> is when each party becomes legally bound to fulfil their obligations under it. A contract is <em>executed</em> over time as each party discharges (or fails to discharge) those obligations.</p>

<p>In a unilateral contract one party fulfils their obligations at the same time as the contract is formed (e.g. returning the lost dog) while the other party must fulfil theirs in the future (e.g. paying the advertised reward). </p>

<p>In a bilateral contract, both parties obligations lie in the future.</p>

<p>Now, these fulfilment of these obligations may lie in the near future (e.g. buying a cup of coffee) or the far future (e.g. a 999-year lease). But that doesn’t change the fact that both of these are bilateral contracts.</p>

<p>In the bilateral example, Alex and Becky choose to engage in business with each other. Alex is aware that he sells to Becky and Becky is aware that she buys from Alex. The terms of the contract (£150 for the bicycle, terms of payment, terms of delivery, etc) are the result of a negotiation between the two.</p>

<p>In the unilateral example, Daniel makes an offer to whoever wants to take it. He doesn't negotiate with anyone - he decided all the terms of the contract on his own. He doesn't have a specific partner in mind - he offers this contract to whoever is willing to agree to his terms.</p>

contract-law