linguistics1-4  Exercise 3: Structure and Heads
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unlockable has two structures, and so two meanings:

  Structure 1:   [ [ un - lock ] - able ]
      First un- joins lock (unlock = undo a lock), then -able joins that.
      Meaning: "able to be unlocked" (a door that can be opened with a key).

  Structure 2:   [ un - [ lock - able ] ]
      First -able joins lock (lockable = able to be locked), then un- joins that.
      Meaning: "not able to be locked" (a door that cannot be locked).

The same string of morphemes means two different things depending on how the
pieces are grouped. That is why morphology needs structure, not just a list.

The head of a compound:

  blackboard   head: board      a kind of board (not a kind of black)
  toothbrush   head: brush      a kind of brush
  Handschuh    head: Schuh      a kind of shoe ("hand-shoe" = glove)

What the head tells you:

  1. The meaning category: a blackboard is a board, a Handschuh is a kind of
     shoe.
  2. The word class of the whole compound (noun here).
  3. In German, the gender: Handschuh is masculine (der Handschuh) because
     the head Schuh is masculine (der Schuh).

The head is the right-hand element in English and German compounds, and the
same is true of Hungarian and Esperanto compounds: vasút and fervojo are both
kinds of "road".