The ICC has paved the way for nations to experiment with four-day Tests, starting with South Africa v Zimbabwe in December. Is this a sign of progress or a degradation of the oldest format? Our writers debate the pros and cons.

Andrew Miller, UK editor

Contrary to popular opinion, the most revolutionary form of international cricket is not T20. It is, in fact, the form that has apparently been spinning in its grave almost since the dawn of its existence. Pick any given era of Test cricket, and you'll hit upon a sport that is not only fundamentally different from any version that pre- or post-dates it, but one that has regularly changed in response - subconsciously or otherwise - to the prevailing trends of the era.

We've had timeless Tests, and six-day Tests, and four-day Tests, even three-day Tests. We've had underarm bowling, and Bodyline bowling - and changes to the laws to counteract both. We've had entire eras played out at a snail's pace (I'm looking at you, the 1960s) and eras in which speed has been of the essence (such as Steve Waugh's pedal-to-the-metal Aussies of the early 2000s).

Now here we are in the T20 age, when batsmen attack and then attack some more - and occasionally come a cropper as a consequence. Are we entertained? Yes, emphatically - whether it's another David Warner new-ball blitzkrieg, or Stuart Broad claiming 8 for 15 in 9.3 overs. Are we short-changed? Only if, as a fan, you've gambled on getting your Test-match fix from the fifth day of a contest. Only two of England's seven home matches in 2017 extended into the fifth and final day, and just two of their last ten Ashes Tests.

Admittedly, one of those was the classic West Indies run-chase at Headingley, which would doubtless be Exhibit A in the defence of the undeniable beauties of a proper five-day finish. But we're deluding ourselves if we think that's the norm these days. The parameters have shifted and, like the scenes in a film that never make the final edit, we cannot be expected to miss grandstand finishes that never actually make it to the silver screen.

"If it helps ease the more urgent and direct conflict in the calendar between T20 leagues and international cricket then it will not be a bad thing"

Instead, the teams might actually revive a facet of the sport that has been cast aside in recent times - the gutsy rearguard, as sides who've been outclassed for three-quarters of a contest rally themselves for a fighting finish, instead of doing what most tend to do in the current climate - settle for another crushing loss and a chance to lick their wounds for an extra day.

Adaptation has been the key to Test cricket's survival for 140 years, and this tweak is just another example. Of course, existential angst compels the format's lovers to fear the worst and yes, it's possible - given the prevailing climate - that what the game loses now will never be restored.

But equally, we just don't know. Our kids' kids may, in 50 years' time, find that they are bored of instant gratification, and want to reinflate the virtues that Test cricket's lifelong defenders know are inherent to the sport. Stranger things have happened. And we know that, because against all expectation after 2278 of the damn things, we still care.

Osman Samiuddin, senior editor

Is it inappropriate to not have an especially strong view on whether Tests should be four or five days? At least not without further data on which contests it is that - and in which venues - are most likely to not require a fifth day. We are getting to know which countries seem to be staging more four-day finishes.

Tests lasting five days in each country since Sep 21, 2012 Host country Tests 5 days Percent UAE 18 16 88.88 SL 25 17 68 BDESH 18 12 66.67 ZIM 9 6 66.67 WI 19 11 57.89 NZ 21 12 57.14 AUS 27 15 55.56 IND 27 14 51.85 RSA 24 11 45.83 ENG 35 15 42.86

But, as one board head suggested in the ICC meetings in Auckland which discussed the issue, perhaps it is more pertinent to identify which contests are likely to not require a fifth day. Perhaps a four-day Test should be scheduled, as the official said, on the basis of a difference in ranking or points between the sides playing. The larger the gap the less likelihood of a Test going five days. This is not foolproof, of course - West Indies winning a Test in England being the most recent example of how this could fail and, in the opposite case, there is the scarcity of recent Ashes Tests that have gone into a fifth day. Could something as sacrosanct as the Ashes really go four days? Any set of rankings or points system would have to be more instantly reflective of form as well as the geography of that form.

In that light, a trial is not a bad way to go about it. Let members decide which Tests will be four and which will be five. And if it helps ease the more urgent and direct conflict in the calendar at the moment between T20 leagues and international cricket then it will not be a bad thing - for one thing, a four-day Test could open up a little more space in the calendar.

Shai Hope celebrates the winning runs Getty Images

George Binoy, deputy editor

Most of the reasons we've been hearing in favour of four-day Tests seem to be administrative- or business-related. While those concerns are important, why aren't more people talking about how the cricket will turn out? Here are some concerns about the proposal, and most of them are about the pitch:

Will the preparation of pitches be monitored more closely in a four-day Test? (Especially in Asia, where unless it's a rank turner from day one, Tests generally accelerate towards a result on days four and five.)

If a home team takes an early lead in a series, what's to prevent them from asking for absolutely flat pitches in the remaining games?

How relevant will spinners be if the surface does not wear as much as it does in a five-day Test?

Will there be steps taken to enforce the greater number of overs in a day/session? Nothing has been done to improve over-rate all these years.

Do we want matches to be held hostage to the weather? Even two sessions lost could kill a result.

Will it lead to more draws? Teams that find themselves in an unwinnable position could more easily bowl/bat for a draw because they can tailor their approach, knowing than the finish line is a whole day closer than day five.

A four-day Test will probably make the format more homogenous: matches like Kolkata 2001 and Adelaide 2006-07, where India and Australia came back from seemingly impossible positions, will all but disappear. Can you win a Test in four days, after conceding 500 in the first innings?

Why would a team declare at 400 for 5, if the pitch is still great for batting at lunch on day two?

Andrew McGlashan, deputy editor

So much apparently needs to be done more quickly these days. Heck, even Twenty20 appears too long for some: a T10 league will launch in the UAE at the end of the year. Therefore, it's felt inevitable that cutting the length of Test cricket would come to fruition, at least for a trial period starting on Boxing Day - a moment in the sporting calendar so often associated with the longer-format's special occasions.

But should it be inevitable? Surely there are better ways to rebalance the game than changing the format that so many still call the 'pinnacle'. For one, doing away with those five-, six- or seven-match one-day series is a good start and will open up space in the calendar. In theory, a one-day series can now be played a week.

Much has been made of the stats that show how many Test matches finish before the dying moments of the fifth day, but even when a Test finishes earlier, the rhythms of the game have developed because there is a fifth day available if needed. Is the prospect of declaration bowling something we really want to consider, or shall we accept that half a day of bad weather could kill off the prospect of a result?

And let's not kid ourselves that players will get their skates on to bowl 100 overs per day. The game has rarely been able to solve its over-rate problem, so it hardly seems sensible to try and squeeze in more into fewer days.

A re-worked ODI programme and plenty of T20 cricket in its various guises gives plenty of options for the time-poor to quick-fix audience. Leave Test cricket alone. It has endured through the ages and can continue to do so.