Why is my MySQL INSERT statement returning an erro

I have an issue with mySQL that I don't really know what is going on. I know it has something to with my Syntax, but not exactly what.

if(isset($_POST['newBtn'])) {
// Check that everything has values and something has been changed
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$title = $_POST['title'];
$smalldesc = $_POST['smalldesc'];
$fulldesc = $_POST['fulldesc'];
// username = $admin
// date = getdate(today in unix time stamp)
date_default_timezone_set('UTC');
$date = new DateTime();
$date = $date->getTimestamp();
if("Testing form. Not relevant.") {
    echo "<div class='alert alert-warning'>You submitted blank data somewhere, or did not change any data from it's default.</div>";
} else {
    $sqladd = "INSERT INTO theories(theory_name,small_desc,full_desc,author,create_date) VALUES ($title,$smalldesc,$fulldesc,$admin,$date)";
    try {
    $sth = $dbh->query($sqladd);

    echo "<div class='alert alert-success'><b>Success!</b>You Have created a new theory that is availible for viewing to the public.</div>";
} catch(PDOExecption $e) {
echo "<div class='alert alert-error'><b>Error!</b>Could not add to database.<br />". $e->getMessage() ."</div>";
}
}
}

and I get this error:

Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax
error or access violation: 1064 You have an error in your SQL syntax; check the manual that
corresponds to your MariaDB server version for the right syntax to use near 'Form,I 
shouldn't be having this much of an issue with php.,I really hate when PH' at line 1' in 
/srv/http/mt-chillad/users/admin-theories.php:42 Stack trace: #0 /srv/http/mt-
chillad/users/admin-theories.php(42): PDOStatement->execute() #1 {main} thrown in 
/srv/http/mt-chillad/users/admin-theories.php on line 42

Yikes, use parameter binding

try {
    $stmt = $sbh->prepare('INSERT INTO theories(theory_name,small_desc,full_desc,author,create_date) VALUES (?, ?, ?, ?, ?)');
    $stmt->execute([$title,$smalldesc,$fulldesc,$admin,$date]);

    // and so on

The error is happening because you are directly inserting unsanitised and un-quoted values into your query.