Image copyright
EPA
Trade negotiations tend not to begin with two sides in agreement - otherwise there would be nothing to negotiate.
So it's not surprising to see the UK and EU set out rather different positions before talks begin in earnest.
In fact, the two sides agree they want a free-trade agreement, with no tariffs (border taxes on goods) or quotas (limits on the amount of goods). They are also keen to include as much of the service sector as possible.
But that's the easy bit and this is likely to become a bruising experience for all involved.
Terms and conditions always apply and the EU says it has two main conditions.
Level playing field
First and foremost, the EU wants the UK to sign up to strict rules on fair and open competition so if British companies are given tariff-free access to the EU market, they cannot undercut their rivals.
These are known as level-playing-field guarantees and they have been a constant theme in the EU's negotiating position for nearly two years.
Most importantly, its draft negotiating mandate says a future partnership must "ensure the application" in the UK of EU state-aid rules on subsidies for business.
The UK would also be required to stay in line with the EU's rules on environmental policy and workers' rights.
But Boris Johnson has publicly ruled out any such commitment and said he would create an independent system that would uphold the UK's international obligations and not undermine European standards.
"There is no need for a free-trade agreement to involve accepting EU rules on competition policy, subsidies, social protection, the environment or anything similar," Mr Johnson said in his speech in London.
He also pointed out the UK spent far less money on state aid than Germany or France.
Canada-style deal?
The EU says without a level playing field, it cannot offer any kind of basic free-trade agreement along the lines of the one it has negotiated with Canada.
The UK's response? A Canada-style deal would be its preference. But if that is not available, it will settle for what Australia has with the EU. In other words, no free-trade deal at all.
Either way, says Mr Johnson, a new relationship will begin on 1 January.
His critics accuse him of recklessness but the prime minister says he has "no doubt that in either case the UK will prosper".
Fisheries
The EU's second condition is a free-trade deal must include an agreement on fisheries - because UK fishing waters are among the best in Europe.
The UK says it's happy to consider a deal on fisheries but it must be based on the notion "British fishing grounds are first and foremost for British boats".
The EU sees things rather differently.
Its draft mandate says a future deal should "aim to avoid economic dislocation for [European] Union fishermen that have traditionally fished in United Kingdom waters".
That's a lot of access and the EU seems prepared to link it to the UK's ability to sell its fish in the EU market.
Fishing is a tiny part of the UK economy - well below 1% - but it has always been an emotional issue. And coastal communities depend on it on both sides of the Channel.
Alignment
When it comes to product standards and other regulations, the EU is more flexible.
"We're not asking for alignment, I know it's a red rag to the UK, so I won't really mention it," the EU's chief negotiator, Michel Barnier said.
"What I am looking for is consistency."
The UK says it must have the right to diverge from EU rules when it chooses to do so but it won't do that just for the sake of doing things differently.
The more it diverges, the more checks there will be and the more barriers to trade will emerge.
Services
That's true for both goods and services. UK financial services companies, for example, will lose the passporting rights that gave them unfettered access to the rest of the EU.
Instead, the UK is hoping for a system of what's known as enhanced equivalence, which would give companies plenty of notice if the rules were about to change.
But talk in government circles of frictionless trade has gone. The UK now accepts that will not be possible outside the EU single market and customs union.
Gibraltar
The EU's negotiating mandate recalls a statement made back in 2018, in which the other 27 member states agreed Gibraltar would not be included in any post-Brexit agreement between the UK and the EU.
It doesn't rule out a separate deal between the UK and the EU that does cover Gibraltar, but that in turn would have to be agreed by the UK and Spain.
This is another hot-button issue pretty much guaranteed to generate tabloid headlines.
Mr Johnson said he would be negotiating for what he called the whole UK family, including Gibraltar.
European Court of Justice
Gaining independence from the rulings of the European Court of Justice (ECJ) was an important part of the argument for Brexit.
Now, the EU is demanding the ECJ be given a legal role in policing any free trade agreement.
It wants the court to be able to issue binding rulings on disputes between the two sides, when they "raise a question of interpretation of [European] Union law".
But the government's written statement says a future agreement cannot include "any jurisdiction for the [ECJ] over the UK's laws".
The ECJ does play a limited role in the withdrawal agreement, both in the special arrangements for Northern Ireland and in resolving any disputes over citizens' rights for the next few years.
But a future trade deal is a different matter.
Other issues
Devising a dispute-resolution system that satisfies both sides will not be easy.
It's not just about trade, it's about internal security cooperation and access to databases too.
"Where a partnership is based on concepts derived from European law," Michel Barnier said, "obviously the ECJ should be able to continue to play its role in full."
The EU's draft mandate also says there should be "automatic termination" of law enforcement and judicial cooperation in criminal matters if the UK were to opt out of the European Convention on Human Rights.
The bottom line for the UK? The ECJ and the EU's legal order "must not constrain the autonomy of the UK's legal system in any way".
Timing
So there are some big divides to be bridged.
Both sides say they would settle for a free-trade agreement but they have to work out how to get there and how to implement it.
It is also worth recalling the government's own internal analysis from November 2018 suggested a Canada-style deal would leave the economy 4.9% smaller after 15 years than if the UK had stayed in the EU.
There is a long way to go in a short period of time.
What claims do you want BBC Reality Check to investigate? Get in touch