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Here is a question from the past exam.
Which of the following words contains an infix?
a. pedicure
b. intangible
c. temptation
d. biology
e. all of the above
An infix is an affix that is inserted into the middle of a base. But I have no idea how to determine whether a word contains an infix.
An infix is anything that is inserted by morphology after the first segment of a morpheme and before the last segment of that morpheme. If you have a morpheme /pot/ and some morphological process stick [l] inside that, e.g. [plot], that is an infix. If you put it before a root, it is a prefix. If you put it after a root, it is a suffix. If you put it before a root then move it to be before the first vowel, i.e. /l+pot/ → [plot], that is a prefix with metathesis.
In order to know if something is an infix, you have to be able to separate a word into constituent morphemes. Sometimes that is trivial and uncontroversial (un+controversial), and sometimes it is controversial (con+tro-vers-i-al?). It is controversial whether the Latin word controversia is divided into contra+versia or contra+ver-ti-a. The problem is that people (including instructors) often conflate "etymologically connected" with "synchronically in an affixation relation". Thgus, join, juncture is a historical example of the concept "infix" (-n- is infixed in Latin in some forms of the root PIE *yug), but there is no process of infixing in modern English that inserts n.
The fact that "none of the above" is not an option tells you that you have to look at this example diachronically, not synchronically, meaning you need to know the Indo-European source of the words.
