many_to_many.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Article extends Model
{

  protected $fillable = ['name', 'content'];

  public function laws()
  {
    return $this->belongsTo(Law::class);
  }

  public function references() 
  {
    return $this->belongsToMany(Article::class, 'article_reference', 'article_id', 'reference_id');
  }

  public function referenced() 
  {
    return $this->belongsToMany(Article::class, 'article_reference', 'reference_id', 'article_id');
  }

}

schema_for_pivot_table.php

<?php
        Schema::create('article_reference', function(BluePrint $table){
            $table->unsignedInteger('article_id');
            $table->unsignedInteger('reference_id');

            $table->foreign('article_id')->references('id')->on('articles');
            $table->foreign('reference_id')->references('id')->on('articles');

            $table->primary(['article_id', 'reference_id']);
        });