Not every position is fixed. An ANCEPS (Latin for ‘two-headed’) is a metrical slot that accepts EITHER a long or a short syllable — marked x. It gives the poet room to breathe inside a strict pattern. Sappho’s own hendecasyllable has one, near its start. Slide across the template and find where the metre lets you choose.
An anceps is a position in a metrical scheme where either a heavy or a light syllable is admissible (notated x, versus — for a fixed long or ≮ for a fixed short). It marks the DEGREES OF FREEDOM in an otherwise fixed template: the Sapphic hendecasyllable (—≮—x—≮≮—≮——) carries an anceps at position 4. Counting anceps positions measures how much choice a metre grants the poet. A fail-loud self-check throws unless the 11-position hendecasyllable has exactly one anceps, at position 4. ◆ the template is exact, node-verified.
The template (including the anceps at position 4) follows the standard analysis; some editors treat other positions as free in certain lines. The concept — a slot open to either weight — is exact; its placement is the metrist’s analysis.