1. Momentum

After the second day at Edgbaston, England had all the momentum. As the series had shown, this is an extremely vulnerable position for a team to be in. England left Cardiff after a near-perfect team performance with too much momentum. The momentum swang a full 360 and knocked them spark out at Lord's, whereupon Australia's counter-momentum back-swang a double-loopie-loop (a technical sports science term), and cleaned them up on the 720-degree reverse slap-round (apologies once again for the necessary use of sports jargon, which only highly qualified experts are able to comprehend).

On the third morning, therefore, England cleverly let Australia's tail-end make a bit of a game of it, then lost a couple of wickets, and chased their target down without too much flourish. They were clearly aiming to decelerate the pendulovelocity of the momentum swingabola down to around the 540-degree mark, to ensure that it would follow through to defeat Australia down in Nottingham with a one-and-a-half somersault clonk-down.

Michael Clarke's clever drop of Ian Bell, at a moment when the departure of England's No. 3 might have prompted some jitteriness, albeit without the real prospect of Australian victory, astutely tried to un-decelerate the momentum back up to the critical 720-ish range. We will know on Thursday which way the momentum has chosen to go - contrary to widely held belief, it is a flighty little beast with a mind of its own - but rest assured, it could mean that one or both of England and Australia have a distinct advantage.

2. The first innings

If these two teams ever conspire to play well in the same match, it could be an all-time classic. In fact, if they manage to play badly in the same match, it could be just as much of an all-time classic. As it is, we have seen a series that has been both compelling and curiously unsatisfying, marked by decisive outbreaks of excellence, and equally decisive outbreaks of rubbishness, as the teams have pitted strength against weakness, and weakness against strength.

Only four times in the last 25 Ashes Tests has the first-innings difference between the two sides been less than 100 runs. (This sequence goes back to the MCG Test of 2006-07. The four matches with a sub-100 first-innings lead/deficit: Perth in 2010-11, when Australia led by 81 in a low-scoring game; the Trent Bridge and Durham thrillers in 2013; and the MCG in 2013-14, when an already thrashed England took an illusory 51-run first-innings lead, added 65 before losing their first wicket, and then subsided like an embarrassed soufflé). The average first-innings lead/deficit in those 25 Tests has been 197.

By comparison, five of the previous nine Ashes Tests had produced a first-innings difference of under 40 runs, and 155 Ashes Tests from 1950-51 up to Perth in 2006-07 had produced 37 games with a deficit of under 50 runs, and 26 more with a difference of less than 100 (40% of the matches). The average first-innings difference was 138, so close first innings have been the exception rather than the norm, but the recent drought is still marked.

Of course, many Tests with evenly matched first innings end up as one-sided powerhoofings, and many Tests with a large deficit turn out to be nail-biting, stomach-churning masterpieces; but this year, as in 2009, the closeness and unpredictability of the series has been in contrast to the lopsided narratives of the individual matches, whose destiny has essentially been all but fixed in the relatively early stages. As fictional TV detective whizz Columbo would no doubt testify, there can be excitement and satisfaction from watching a drama progress to an ending that has already been decided; there is also a reason why most TV detective shows do not reveal the result until right at the end.

"The momentum swang a full 360 and knocked them spark out at Lord's, whereupon Australia's counter-momentum back-swang a double-loopie-loop (a technical sports science term), and cleaned them up on the 720-degree reverse slap-round"

If England/Australia repeat their strength/weakness that was so potently on display at Lord's/Edgbaston, then they will be well on the way to another vital defeat/victory (delete according to preference).

3. Michael Clarke's batting position

Where should Clarke bat in the remainder of the series? Would dropping down to No. 5, where he has had most success as a Test player, be a sign of weakness? Would staying at No. 4 be a sign of insanity? Is "on the beach" an option? The answers: (a) perhaps, but it might be very vocally suggested to be a sign of weakness, even if it isn't, and could therefore become accepted as a sign of weakness, regardless of whether or not it actually is; (b) perhaps, but No. 5 has been a highly productive position in the Test batting order for many countries in recent years, so playing one of your best players at five could make sound run-making sense; (c) no, but it would be preferable to "on the plane", where Clarke claimed he has been playing in the first three Tests. He could bat at four and succeed, or bat at five and fail. Or vice versa.

The mantra "class is permanent, form is temporary" undoubtedly has an element of truth, without being an immutable law of science (hence the reason WG Grace no longer plays for England). But the facts remain that class players can have elongated stretches of poor form (as Ian Bell has proved over the last two years, and many before him, including Lara and Tendulkar), and even class players some day reach the end of the physical road. Whether or not Clarke has yet done so is open to question. Back injuries are notoriously unhelpful for batsmen. Whether he bats at four or five, he will remain a "class player". But he could also remain horrifically out of form. Or score a century. This is clearly a potentially critical issue for both England and Australia.

4. Key players missing

If Australia having been struggling without the self-admittedly effectively absent Michael Clarke, then they have been missing the actually absent Ryan Harris like a dolphin would miss its blowhole, or a unicyclist would his seat.

England could find life similarly awkward without Jimmy Anderson. He has a mixed record against Australia, averaging close to 36, but has played a major role in several important victories in England's victorious series (he took four of the top six in the decisive first innings at Lord's in 2009; Ponting and Clarke in his first seven balls in Adelaide in 2010, and four more in the match; four in the first-day skittling at the MCG later that series, then seven in the match in Sydney; and, most significantly, five in each innings at Trent Bridge two years ago).

His absence at Trent Bridge could be a vital boost for Australia. Or open the door for a replacement to have a Finn-like impact on the series.

5. Brittle batting

It could all come down to which team is able to play an entire Test match, spanning as many as two innings, without at any point being skittled out in under 40 overs.

Following England's historically awful 37-over fourth-innings floundering at Lord's, Australia's 36.4 over capitulation at Edgbaston was the sixth swiftest dismissal of a team in the opening innings of an Ashes Test. (Since 1902, the only more rapid first-day disintegrations have been Australia's Darren Gough-inspired 31.5-over subsidence on day one of the 1997 Ashes, and England's woeful 33.5-over capitulation at Leeds in 2009.)

One of the rules of Test cricket is "Do not get skittled out in under 40 overs." The team that adheres to this rule will hold a decisive edge.

Michael Clarke walks off after another cheap dismissal Getty Images

CONFECTIONERY STALL TRENT BRIDGE PREDICTION: I just don't know any more. England, maybe?

Wherever Clarke bats - he will be under equal pressure in either position - he is unlikely to match the spectacular batting-order migrations of one of his predecessors as Australia captain. On the 1956 Ashes tour Ian Johnson, an offspinning just-about-allrounder who began his Test career in the middle order but latterly batted mostly at 9 or 10, managed to bat in all seven positions from five down to 11 in just five Tests.

He began the series at eight, batted at nine in the second Test, then 10 and seven in the third, and 11 and 10 in the fourth. Having amassed the scoreboard-shattering total of 39 runs at an average of 5.5, he then took the somewhat counter-intuitive step of promoting himself to No. 5 in the first innings of the final Test. Having evidently noticed the opportunity for a small piece of batting-order history, he then batted at six in the second innings. In all: 61 runs at 7.6. But what a journey. Add in six wickets at an average of just over 50 (four of them for 151 runs at Old Trafford, on the pitch where his England offspinning counterpart Jim Laker took 19 for 90 in the match), not to mention zero catches, and losing four tosses out of five, and it is clear that Johnson set a benchmark for "on the plane" captaincy even in the days before touring cricket teams travelled by air.

Some Edgbaston stats

● Steven Finn's glorious return was a great story, a great personal triumph, and a great relief. He bowled like the bowler he looked like he had become when taking four in each innings against South Africa at Lord's in 2012 (seven of his wickets were top-order batsmen). Edgbaston was his fifth Ashes Test. The previous four had been marked by both wickets and run-leaking, giving him Ashes career stats that are now a one-man incarnation of the spirit of 21st-century cricket - of the 116 bowlers with 20 or more Ashes wickets since the First World War, Finn currently has the best strike rate (40.9), the 50th best average (29.08) and the 116th best economy rate (4.26).

● Anderson was the first England bowler to take six in the opening innings of an Ashes Test in this country since Peter Such's debut 6 for 67 in 1993, and the first England seamer to do so since Richard Ellison's 6 for 77, also at Edgbaston, in the fifth Test of 1985.

● Ian Bell became the first England No. 3 to score two fifties in an Ashes Test since Robin Smith, at Trent Bridge, in 1993.

● Stuart Broad batted for 50 balls in a Test innings for the first time since the Old Trafford Test in 2013, an innings of valuable and overdue restraint, and the first time he appears to have batted like a batsman for a considerable time.

● This is the second successive Ashes in which David Warner has scored 50 or more in the second innings of the first three Tests. Previously, only Herbert Sutcliffe had done so, in 1924-25.

● Currently, only one bowler in this series is conceding less than three runs per over - Adam Lyth. From his one over of niggardly Yorkshire-hewn neo-Illingworthian offspin.