As far as I can tell, the only difference between these two ways of describing classes of words is that 'syntactic categories' actually relies on evidence of use for determining categories, while 'parts of speech' labels can just be applied without any appeal to evidence. There is also the term 'word classes' which appears to be similar, but also used without specification. Are they simply used by different sub-disciplines of linguistics? Or are there more specific differences?

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    interesting question. you might add the term "word classes" to the list.
    – user483
    Jul 18, 2013 at 23:52
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    There are "traditional" categories called "Parts of Speech", which is an English translation of Latin Partes Orationis, which Donatus used. There are "traditionally" eight, but not the same eight as Donatus used; Roman grammarians didn't think adjectives and nouns were different enough to count separately. On the other hand, they thought participles were different enough from verbs to be worth their own pars orationis
    – jlawler
    Jul 19, 2013 at 1:19
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    And then there are syntactic categories, which come in many flavors and colors and are sometimes based on data and evidence, and are sometimes just whatever is convenient for a particular theory. Or for a particular parser and tagger.
    – jlawler
    Jul 19, 2013 at 1:21
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    This may or may not be official, but the way I see things: A "part of speech" is a category a word falls into, regardless of context. eg "Ball" is always a noun. Syntactic categories are ways of describing the parts of a sentence/piece of text, and can be words or phrases. eg. Subject, verb, object etc. So there is some overlap (ie "Verb" is both, but the syntactic category "Verb" may be a phrase, not a word). "Ball" can now be either the subject, the object, or something else entirely, depending on the sentence we're analysing.
    – Ryno
    Jul 19, 2013 at 2:11
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    Technically, "technically" is not a technical word. Saying a noun and verb derived from the same etymology are not the same word is likely not to be a universally accepted fact. It depends on the definition of "word", which we all know is the trickiest term in linguistics. Jul 24, 2013 at 0:29

4 Answers 4


The term part of speech is narrower than the term syntactic category. Every part of speech is a syntactic category, but many syntactic categories are not parts of speech. This holds particularly of the distinction between word and phrase. Words are parts of speech, but phrases are not. A noun is a part of speech and a syntactic category, whereas a noun phrase is a syntactic category but not a part of speech. An adjective is a part of speech and a syntactic category, whereas an adjective phrase is a syntactic category but not a part of speech. Thus the term part of speech denotes a subgroup inside the greater group denoted by syntactic category.

  • Great, that makes sense. Do you also have any thoughts on word classes?
    – LaurenG
    Jul 23, 2013 at 22:05

I hazard the following answer. If you will consider for a moment, parts of speech are word categories, and can be used to create phrases. So they are essentially phrase-level syntactic categories, functional modifications necessary to make correct phrases. The concept of "syntactic category," if I am not mistaken, includes these plus sentence level concepts like subject, object, predicate, clause, etc. A noun is a word root so modified morphologically or simply by word position as to be capable of heading a noun phrase, combine with adjectives, or other functional roles; but a NP as such has no "subject" nor is one in itself. "Subject" is a sentence-level functional category. In the modern sense this a syntactic category. Of course in languages like Latin sentence level morphology is built into words through inflection. If you take the phrase puella bona you have an item morphologically marked for functional role as sentence subject. But it is of course still only a noun phrase and not an actual subject. And puella can never head a VP or PP, not because of its inflection, but because it is a noun.


What follows is just my impression.

Syntactic category is a term that has a formal definition in a few grammar formalisms. In contrast, "part of speech" is the intuitive class of a word. I suppose the equivalent term for syntactic category in HPSG would be Typed Feature Structures or just signs.

In CCG, for example, the syntactic category S\NP refers to many things: intransitive verb, transitive verb with the object filled-in, a modified verb phrase, etc.

As another example, given the phrases "young Obama" and "Barack Obama", a (trained) person may tag "young" as adjective and "Barack" as noun. However, in CCG, they are both N/N.

  • so does HPSG specifically think of 'part of speech' as an intuitive word class? Or is this from some other theory?
    – LaurenG
    Jul 23, 2013 at 21:59
  • @LaurenG: It's the former, but 'intuitive' is a subjective term. You can find a longer explanation on page 28 of webspace.utexas.edu/wechsler/HPSG-COURSE-PACKET.pdf
    – prash
    Jul 24, 2013 at 11:20

Definitions of parts of speech and syntactic categories have already been given by Tim Osborne. I would like to add a point on whether there is any evidence to label a word a noun or a preposition, since this is also occurred in question.

Let's say we already know that table is a noun. Then we can take a sentence where this word occurs and try to replace it with other words. If the sentence is still grammatical then the new word is also a noun. For example,

  1. The mouse is under the table.
  2. The mouse is under the bucket.
  3. The mouse is under the behind.

bucket is also a noun since sentence 2 is grammatical, behind is not a noun since sentence 3 is not grammatical. In this way all words can be assigned to parts of speech.

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    The problem with this diagnostic is that many words have senses in multiple word classes. And in fact "behind" is such a word as it has a couple of noun senses which can make 3. grammatical. Most obviously it can mean "buttocks". Jul 23, 2013 at 1:19
  • Good point, although I'd say it's not a bug, it's a feature ;) If there are homonyms then any sound parts of speech diagnostic should include that aspect.
    – robert
    Jul 23, 2013 at 1:24
  • I believe the usual way to deal with such issues is to use as many diagnostics as possible and analyse the results as a whole. Some based on morphology, some based on syntax, etc. Jul 23, 2013 at 1:29
  • I'm fine with using diagnostics (and the many problems that come from that)- but is your process telling me that 'table' is a part of speech or a 'syntactic category'?
    – LaurenG
    Jul 23, 2013 at 21:58
  • It tells you that 'table' is a noun, i.e. a part of speech. A test for syntactic category would be 'The mouse is under X'. For example, 'The mouse is under the table', 'The mouse is under my car', but *'The mouse is under was eating' is ungrammatical, since 'was eating' is a verb phrase.
    – robert
    Jul 24, 2013 at 19:22

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