Is "Everyone is welcome along." a valid sentence?

Solution 1:

I want to say no, but I can't back that up with a "why," aside from the fact that I've never heard it before.

However, "you're welcome to come along" definitely is acceptable and commonly used. It is used when, say, someone's going to the store to buy something. They may say to their friend, "you're welcome to come along," if they desire (or wouldn't mind) their friend's company to the store.

(EDIT: That said, I don't think that "everyone is welcome along" would be totally unheard of. The context I would expect that to be in similar context to "everyone is welcome to come along," above.)

Solution 2:

There is absolutely nothing ungrammatical about "welcome along" whatsoever.

The performative adjective "welcome" standardly takes locative preposition phrases as Complements. The preposition phrase indicates the location of the speaker or that which the addressee is headed towards. Sometimes the prepositions take noun phrase Complements, sometimes they take preposition phrases as Complements and sometimes they take no Complement at all—in other words they are intransitive. Here are some examples with preposition phrases containing noun phrase Complements:

• Welcome to our humble abode!
• Welcome aboard the Boeing 787 Dreamliner!
• Welcome onto the Team Joe!

Some examples with prepositions taking preposition phrase Complements:

• Welcome back from the spring break!
• Welcome down to paradise rock.
• Welcome through to the other side.

Some examples with intransitive uses of prepositions:

• Welcome back!
• Welcome aboard!
• Welcome through!
• Welcome ashore!
• Welcome down!
• Welcome home!
• Welcome along!

Welcome along is particularly used when somebody is being welcomed to an activity or journey for the first time. We find, therefore examples such as this one from the University of Edinburgh with the title "Welcome along /back" where they greet new students and welcome back returning ones.

As "welcome" is a performative (by saying the word you perform the action it describes), it is far more common in spoken English and on signs and brochures than in formal written texts. There's not much point in looking up such phrases on Google books therefore.

Welcome along is certainly not formal in tone. However, that is completely irrelevant to whether it is grammatical or not. It is, of course, perfectly grammatical. How do we know? Because native speakers of English use it!

^{Thanks to Mari-Lou A for Welcome home}

Solution 3:

Everyone is welcome aboard [the ship, vessel, plane, etc. or metaphor thereof].

/The captain welcomed guests aboard [the ship]/.

In that sentence, aboard is a preposition in the implied phrase. It is not a single adverb as it would be in: to ships came close aboard. It's an adverbial phrase.

/Everyone is welcome to come along [with me, them, etc.]/ is grammatical. Leaving out the to is non-standard and may be regional. I have never heard it before reading it here. For me, to /come along/ is either a semi-phrasal verb or a prepositional phrase.

/They are welcome to come along [with you]/: semi-phrasal verb in an implied preposition phrase.

/They came along later in the day [to the school]/: a semi-phrasal verb, often seen in BrE, to mean come to a place. Similar to pop around and show up (AmE). Same as previous sentence.

come along is the semi-phrasal verb for the non-phrasal verb accompany: /He came along to the school with me/ = He accompanied me to the school.

For me, a semi-phrasal means the verb actually implies a prepositional phrase that has been dropped over time.

For example: to stand up meaning to stand on one's feet in a vertical position is not a semi-phrasal verb versus to come along [with me] is.

The implied prepositional phrases are adverbial.