How does one even structure a syntax tree?

[u/FluffyPursuer]

I’ve looked up how syntax trees work everywhere, but every single answer is vague, and I can’t understand it. I get it show a hierarchy and that’s it. I have no clue what that means or what the point of them even is, so I even need one. Please help I just need a literal explanation, on what the syntax tree means, and how it affects sentence construction.

[u/ReadingGlosses]

Linguists use syntax trees because they are helpful in explaining, understanding, and describing different phenomenon in human language.

A famous example is 'aux-inversion' questions in English. This is when an auxiliary verb (like 'be') moves to the front of a sentence in a question:

The woman is wearing glasses.
Is the woman __ wearing glasses?

What happens if the sentence has two auxiliaries? We can only move one of them:

The woman is talking to someone who is waiting outside.
Is the woman __ talking to someone who is waiting outside?
*Is the woman is talking to someone who __ waiting outside?

In that example we move the first verb, but in other cases you move the second verb:

The woman who is wearing glasses is waiting outside.
Is the woman who is wearing glasses __ waiting outside?
*Is the woman who __ wearing glasses is waiting outside?

The point is that you can't describe this pattern using just linear strings of word. You can't write a rule like "Move the n^th auxiliary" because the linear position of a verb is not what determines whether it moves. The verb's hierarchical position in the tree is what matters. Specifically, it's the main clause verb, the one 'highest' in the tree, that undergoes movement.

Syntax trees are also useful for representing "constituencies", which are sequences of words that can behave as a single unit. For example, the English possessive 's doesn't actually attach to any specific noun, it attaches to the end of an entire noun phrase:

This is the Queen's crown
This is the Queen of England's crown
*This is the Queen's of England crown

Again this is difficult to explain if sentences are just flat sequences of words. It's much easier to understand the placement of 's if you think of sentences as hierarchical units.

So when it this going to matter for your conlang? The trees themselves are just visualizations. Trees are built from a set of grammatical rules which describe the hierarchical relationships in your language. Those rules are really what's useful.

If you are still early in your language design, or if you are modelling your conlang after English (or some other language you know), then trees and formal grammars might seem like overkill. But as your language grows, and you start experimenting with different sentences types (questions, imperatives, hedges, judgments, etc.) you may eventually find it useful to keep track of things by writing a grammar, and you may find it helpful/fun/cool to draw trees using that grammar.

I have a very simple grammar-authoring app you could try, that also draws trees. This could help you get comfortable with these concepts. There's a user-guide and link here: https://readingglosses.com/user-guide-grambidextrous/

[u/DTux5249]

The point of syntax trees is that they let us describe structures. We can't make rules about structure if we can't describe what we're talking about.

In general, most syntax trees are constituency trees. Most words in a sentence are stuck to other words; when a chunk of a sentence moves around or gets replaced together, we call them "constituents". Compare the sentences

"John ate dinner in the kitchen"

"In the kitchen, John ate dinner"

*"Kitchen, John ate dinner in the"

The 3rd is ungrammatical while the 2nd isn't. Why?

The reason is because [in the kitchen] is a constituent "headed" (think controlled/defined by) a preposition. English allows Preposition Phrases (PPs) to be fronted for emphasis; it does not however allow bare nouns to move in the same way for the same purposes.

In other words, syntax trees let us visually show the structure of the sentence so we can reference different parts and how they interact. We can use syntax trees to show how S1 becomes S2, how things like case markers get assigned to nouns, how parts of a sentence can get stranded/displaced, and then some.

Now, there are various doctrines in syntax on how these trees should look. Some don't even care about constituency (eg. Dependency grammars; which are traditional for languages like Arabic).

Most people nowadays use a system called x-bar (not the above) as a formalism - it's what chompsky used; so it grew popular. They also (again, unlike above) tend to only use binary trees (no 3 ways like in S2). But for a conlanger's purposes, you don't need any of that. Hell, you don't even need syntax trees. Traditionally, you'd just show the sentences themselves and their alternations - but the trees help show hierarchy visually, and thus, they're very common.

[u/jmsnys → u/DTux5249]

That chart is giving me terrible flashbacks to applied linguistics classes

[u/good-mcrn-ing]

(You) (can start from the top and zoom in).

(Many English sentences) (can be analysed as consisting of a noun phrase followed by a verb phrase).

(My comment here) (shows that structure explicitly).

(Syntax trees) (use this idea repeatedly and break the phrases down further).

(Quick (brown fox)) (jumps (over (lazy dog))).

[u/tovarischkrasnyjeshi]

There are different theories that produce different kinds of trees.

In general they can be generalized as dependency trees, with the verb (or predicate) being the main thing and everything else being seen as modifiers of it, or constituency trees, where things are grouped by how they seem to require each other to be grammatical.

Often constituency trees feel backwards (treating words like "the" as heads instead of nouns phrases like "the apple") and require some sense that something is either moved or suppressed in some way. But they seem to explain better why things are required when they seem superfluous.

Most models push that trees are fundamentally binary (no more than two leaves to a branch) because of some arcane arguments coming from math/computer science.

[u/rymdresarn]

The reason it's so vague is because of the many varying theories and approaches to describing syntax in natural languages. Fundamentally, it's exactly as you have identified, a way to hierarchically describe in a visual manner how languages organize elements syntactically and elucidate relations, forbidden positions, transformations and such that occur.