Metric accent

Count "one, two, three; one, two, three" out loud. Without anyone asking, the "one" comes out stronger than the rest. That weight, returning at the start of every measure, is metric accent: the alternation of strong and weak beats.

It is not written in the score (Med 1996, ch. XXII). No sign marks the first beat as strong; a reader knows it is, simply because it is first. That is why a measure of three and a measure of two sound different even when every note has the same length: the weight comes back every three beats in one, every two in the other.

In this topic's examples, the player strikes the first beat harder than the others, so the weight can be heard.

Strong and weak in each meter

In duple meter, the first beat is strong and the second weak.

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In triple meter, the first is strong and the other two are weak.

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In quadruple meter, the first is strong, the third is medium-strong, and the second and fourth are weak (Lacerda 1966, ch. VI).

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Listen to the third beat of the quadruple measure: it weighs less than the first but more than the second and fourth. That is what makes quadruple meter sound like two duple measures glued together, one with a larger stress and one with a smaller.

Meter	Beat 1	Beat 2	Beat 3	Beat 4
duple	strong	weak
triple	strong	weak	weak
quadruple	strong	weak	medium-strong	weak

Larger measures follow the sum that makes them. Lacerda hears five as three plus two, or the reverse, and seven as four plus three, or the reverse; the first beat of each part gains weight (Lacerda 1966, ch. VI).

The books disagree about triple meter

Lacerda and Med give triple meter as strong, weak, weak. Blatter sees more nuance: a three-beat bar may carry a secondary accent, and it may fall on either the second or the third beat. For him, the place of that accent, or its absence, is exactly what gives each piece in three its characteristic feel (Blatter 2007, part 1, art. 4).

Both readings fit what the ear hears. A waltz tends to lean only on the first beat; other dances in three, such as the mazurka, often shift a stress onto the second or third. The general rule is strong-weak-weak; the rest is style.

Blatter also names meters differently: he calls a four-beat bar duple, since it is built of twos, where the Portuguese books keep quadruple as a meter of its own.

Parts of the beat have weight too

Accent does not stop at the beat. When a beat divides, its first part is strong and the others weak (Lacerda 1966, ch. VII). In simple meter, each beat divides into two parts, strong and weak:

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In compound meter, into three: strong, weak, weak.

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Med arranges this in two levels. The accents of the beats are principal; those of the parts of the beat are secondary. At a slow tempo the secondary accents come through clearly; at a fast one they nearly vanish, and the ear keeps only the principal ones (Med 1996, ch. XXII).

The names of strong and weak

The strong beat goes by several names. Med records the Portuguese "apoio", thesis and "repouso"; the weak beat, "impulso", arsis and "lance" (Med 1996, ch. XXII). The Greek names come from dance and verse: the thesis was the foot coming down, the arsis the foot lifting. Blatter uses the English equivalents, downbeat for the first beat and upbeat for the last, which prepares the return of the first.

What comes next

When a note starts on a weak beat and carries on into the strong one, the weight leaves its expected place. That displacement is syncopation. And when music starts before the first strong beat, on a weak one, it starts with an anacrusis.