Local rivals often like to imagine themselves opposites of each other. Every now and again they actually might be.
Arsenal and Tottenham meet in a peak and a trough respectively, as the two north London sides showed in the Champions League.
The Gunners, 3-2 victors against Ludogorets, are in fine form, winning 10 of their last 11 games and unbeaten in 15.
Spurs, beaten 1-0 by Bayer Leverkusen, have lost the verve they exhibited when they overwhelmed Manchester City. They are winless in six.
Now they owe their lofty position to their defensive resilience, Arsenal to their prowess going forward.
So the battle for supremacy in north London could come to a contest between attack and defence, between irresistible force and immovable object.
Arsenal's forwards are elusive and excellent, with supposed striker Alexis Sanchez dropping off and others accelerating into the space he leaves, with Mesut Ozil at his creative best. Olivier Giroud is fit and firing again and the Frenchman adds the extra dimension a target man provides.
Tottenham's defence is terrifically well-drilled. They have conceded only one goal in open play in the Premier League this season.
They have actually improved their defensive record while switching to a more adventurous system, from 4-2-3-1 to 4-1-4-1. They boast two of the most progressive full-backs in the division in Kyle Walker and Danny Rose.
It is why they could reject the implication they are puritans. They rarely concede, but they have had the most shots in the division.
The problem is that too many have come from long range and too many have been comparatively harmless.
Tottenham's attacking midfielders tend to converge infield, which produced a blur of brilliant movement when they beat City, but has looked more a case of congestion and confusion since then.
Whereas Arsenal have scored 18 goals in their last six games, Tottenham have mustered a mere three. The injured Harry Kane's return cannot come quickly enough.
Tottenham face questions, the sort sides who have progressed and then stumbled encounter: Have opponents worked them out?
An answer in the negative may be supplied if Christian Eriksen returns to his best.
In any case, their style of play is so fashionable that Arsenal, so often their antithesis during Arsene Wenger's long reign, appeared to have borrowed from them.
Their renaissance owes much to playing with more pace and fluidity in attack and adding more bite in midfield.
There was a time last season when Tottenham seemed like tomorrow's team and Arsenal yesterday's men.
And yet, in time-honoured tradition, Arsenal rallied to finish ahead of their neighbours, as they have done every year in Wenger's reign, aided by Spurs' capitulation in a 5-1 final-day defeat at relegated Newcastle.
Now Arsenal are very much in the ascendancy again. They are favourites. The only unbeaten record in the Premier League is under grave threat.
ARSENAL V TOTTENHAM
Singtel TV Ch103 & StarHub Ch228, tomorrow, 7.55pm