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Override for the tutor's lesson content generation calls. Auto uses the system default (Claude Sonnet 5 for lesson text, Opus 5 for diagrams).

Lesson generation model

System default

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Tutoring abilities

Imagine you walk up to a locked door. Do you have the strength to kick it open, the permission to unlock it, or is there just a chance it opens on its own?

In English, tiny helper words called **modal auxiliaries** change the entire mood of a sentence to tell us about **ability**, **permission**, or **possibility**.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="aspect-ratio" content="4:3">
<style>
  * { box-sizing: border-box; margin: 0; padding: 0; }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background: #f8f9fa;
    color: #1e2945;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    padding: 12px;
  }
  .app-container {
    width: 100%;
    max-width: 480px;
    display: flex;
    flex-direction: column;
    gap: 12px;
  }
  .modal-nav {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 8px;
  }
  .modal-btn {
    background: #ffffff;
    border: 2px solid transparent;
    box-shadow: 0 1px 3px rgba(0,0,0,0.08);
    border-radius: 10px;
    padding: 10px 4px;
    font-size: 17px;
    font-weight: 700;
    color: #1e2945;
    cursor: pointer;
    text-align: center;
    transition: background 0.2s, box-shadow 0.2s, color 0.2s;
  }
  .modal-btn.active {
    background: #22b7ff;
    color: #ffffff;
    box-shadow: 0 4px 12px rgba(34, 183, 255, 0.35);
  }
  .visual-stage {
    background: #ffffff;
    border-radius: 12px;
    padding: 16px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.06);
    display: flex;
    flex-direction: column;
    gap: 14px;
    min-height: 230px;
  }
  .sentence-display {
    text-align: center;
    font-size: 20px;
    font-weight: 600;
    color: #1e2945;
    padding: 12px 8px;
    background: #f1f5f9;
    border-radius: 10px;
  }
  .highlight-word {
    color: #0284c7;
    font-weight: 800;
    border-bottom: 2px solid #0284c7;
    padding: 0 2px;
  }
  .mood-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 8px;
  }
  .mood-card {
    background: #f8f9fa;
    border-radius: 10px;
    padding: 10px 6px;
    text-align: center;
    opacity: 0.28;
    transition: opacity 0.3s, background 0.3s, transform 0.3s;
  }
  .mood-card.active {
    opacity: 1;
    background: #e0f2fe;
    box-shadow: 0 2px 6px rgba(34, 183, 255, 0.2);
  }
  .mood-icon {
    font-size: 24px;
    display: block;
    margin-bottom: 4px;
  }
  .mood-title {
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    color: #475569;
  }
  .mood-card.active .mood-title {
    color: #0369a1;
  }
  .mood-tag {
    font-size: 11px;
    font-weight: 600;
    margin-top: 4px;
    color: #0284c7;
    background: #ffffff;
    padding: 2px 4px;
    border-radius: 4px;
    display: inline-block;
  }
  .time-bar {
    display: flex;
    align-items: center;
    justify-content: space-around;
    padding: 8px 12px;
    background: #f8f9fa;
    border-radius: 8px;
    font-size: 13px;
    font-weight: 600;
    color: #64748b;
  }
  .time-badge {
    padding: 4px 10px;
    border-radius: 6px;
    transition: background 0.2s, color 0.2s;
  }
  .time-badge.active {
    background: #22b7ff;
    color: #ffffff;
    font-weight: 700;
  }
</style>
</head>
<body>
<div class="app-container">
  <div class="modal-nav">
    <button class="modal-btn active" data-modal="can">Can</button>
    <button class="modal-btn" data-modal="could">Could</button>
    <button class="modal-btn" data-modal="may">May</button>
    <button class="modal-btn" data-modal="might">Might</button>
  </div>

  <div class="visual-stage">
    <div class="sentence-display" id="sentenceBox">
      I <span class="highlight-word">can</span> swim 🏊
    </div>

    <div class="mood-grid">
      <div class="mood-card active" id="cardAbility">
        <span class="mood-icon">💪</span>
        <div class="mood-title">Ability</div>
        <div class="mood-tag" id="tagAbility">Present</div>
      </div>
      <div class="mood-card active" id="cardPermission">
        <span class="mood-icon">🙋</span>
        <div class="mood-title">Permission</div>
        <div class="mood-tag" id="tagPermission">Informal</div>
      </div>
      <div class="mood-card" id="cardPossibility">
        <span class="mood-icon">🎲</span>
        <div class="mood-title">Possibility</div>
        <div class="mood-tag" id="tagPossibility">—</div>
      </div>
    </div>

    <div class="time-bar">
      <span class="time-badge active" id="badgePresent">⚡ Present / Future</span>
      <span class="time-badge" id="badgePast">⏳ Past</span>
    </div>
  </div>
</div>

<script>
  const data = {
    can: {
      sentence: 'I <span class="highlight-word">can</span> swim 🏊',
      ability: { active: true, tag: 'Present' },
      permission: { active: true, tag: 'Informal' },
      possibility: { active: false, tag: '—' },
      time: 'present'
    },
    could: {
      sentence: 'I <span class="highlight-word">could</span> run fast 🏃',
      ability: { active: true, tag: 'Past' },
      permission: { active: false, tag: '—' },
      possibility: { active: true, tag: 'Possible' },
      time: 'past'
    },
    may: {
      sentence: 'You <span class="highlight-word">may</span> enter 🚪',
      ability: { active: false, tag: '—' },
      permission: { active: true, tag: 'Polite' },
      possibility: { active: true, tag: 'Likely' },
      time: 'present'
    },
    might: {
      sentence: 'It <span class="highlight-word">might</span> rain 🌧️',
      ability: { active: false, tag: '—' },
      permission: { active: false, tag: '—' },
      possibility: { active: true, tag: 'Uncertain' },
      time: 'present'
    }
  };

  const buttons = document.querySelectorAll('.modal-btn');
  const sentenceBox = document.getElementById('sentenceBox');
  const cardAbility = document.getElementById('cardAbility');
  const cardPermission = document.getElementById('cardPermission');
  const cardPossibility = document.getElementById('cardPossibility');
  const tagAbility = document.getElementById('tagAbility');
  const tagPermission = document.getElementById('tagPermission');
  const tagPossibility = document.getElementById('tagPossibility');
  const badgePresent = document.getElementById('badgePresent');
  const badgePast = document.getElementById('badgePast');

  function updateModal(key) {
    const item = data[key];
    sentenceBox.innerHTML = item.sentence;

    cardAbility.classList.toggle('active', item.ability.active);
    tagAbility.textContent = item.ability.tag;

    cardPermission.classList.toggle('active', item.permission.active);
    tagPermission.textContent = item.permission.tag;

    cardPossibility.classList.toggle('active', item.possibility.active);
    tagPossibility.textContent = item.possibility.tag;

    badgePresent.classList.toggle('active', item.time === 'present');
    badgePast.classList.toggle('active', item.time === 'past');
  }

  buttons.forEach(btn => {
    btn.addEventListener('click', () => {
      buttons.forEach(b => b.classList.remove('active'));
      btn.classList.add('active');
      updateModal(btn.dataset.modal);
    });
  });
</script>
</body>
</html>

How do we talk about the skills we have right now versus skills we had in the past?

We use **can** to show that someone is able to do something right now in the present.

For example, "Maya **can** swim across the pool" shows present ability. **When Leo** was four, he **could** ride a bicycle, describing past ability.

For instance, "Maya can swim across the pool" describes present ability. **When Leo** was four, he could ride a bicycle shows past ability.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    }

    body {
      background: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      padding: 12px;
      user-select: none;
      -webkit-user-select: none;
    }

    .main-stage {
      width: 100%;
      max-width: 420px;
      display: flex;
      flex-direction: column;
      gap: 16px;
      align-items: center;
    }

    /* Tab Switcher */
    .timeline-nav {
      display: flex;
      background: #e2e8f0;
      padding: 4px;
      border-radius: 24px;
      width: 100%;
      max-width: 320px;
      gap: 4px;
    }

    .nav-btn {
      flex: 1;
      border: none;
      background: transparent;
      padding: 8px 12px;
      font-size: 14px;
      font-weight: 600;
      color: #64748b;
      border-radius: 20px;
      cursor: pointer;
      transition: all 0.25s ease;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
    }

    .nav-btn.active {
      background: #ffffff;
      color: #2563eb;
      box-shadow: 0 2px 6px rgba(0, 0, 0, 0.08);
    }

    /* Display Card Container */
    .viewport {
      width: 100%;
      height: 240px;
      position: relative;
      overflow: hidden;
      border-radius: 16px;
      background: #ffffff;
      box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
      border: 1px solid #e2e8f0;
    }

    .scene-panel {
      position: absolute;
      inset: 0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 14px;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.35s ease, transform 0.35s ease;
      transform: scale(0.96);
    }

    .scene-panel.active {
      opacity: 1;
      pointer-events: auto;
      transform: scale(1);
    }

    /* Modal Badge */
    .modal-tag {
      font-size: 20px;
      font-weight: 800;
      letter-spacing: 0.5px;
      padding: 6px 20px;
      border-radius: 12px;
      text-transform: uppercase;
    }

    .tag-can {
      background: #eff6ff;
      color: #2563eb;
      border: 2px solid #bfdbfe;
    }

    .tag-could {
      background: #fef3c7;
      color: #d97706;
      border: 2px solid #fde68a;
    }

    /* Visual Scene Components */
    .scene-visual {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 8px;
    }

    .avatar-icon {
      font-size: 56px;
      line-height: 1;
      filter: drop-shadow(0 4px 6px rgba(0, 0, 0, 0.1));
    }

    .time-chip {
      font-size: 13px;
      font-weight: 700;
      color: #64748b;
      background: #f1f5f9;
      padding: 4px 10px;
      border-radius: 20px;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }

    /* Bottom playback / step indicators */
    .controls {
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .dot {
      width: 10px;
      height: 10px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: all 0.25s ease;
      border: none;
      padding: 0;
    }

    .dot.active {
      background: #2563eb;
      width: 24px;
      border-radius: 5px;
    }
  </style>
</head>
<body>

  <div class="main-stage">
    
    <div class="timeline-nav">
      <button class="nav-btn active" id="btn-now" onclick="setMode(0)">
        <span>⏱️</span> Present
      </button>
      <button class="nav-btn" id="btn-past" onclick="setMode(1)">
        <span>📅</span> Past
      </button>
    </div>

    
    <div class="viewport">
      
      <div class="scene-panel active" id="panel-0">
        <div class="modal-tag tag-can">CAN</div>
        <div class="scene-visual">
          <div class="avatar-icon">🏊‍♀️</div>
          <span class="time-chip">Maya · Present Ability</span>
        </div>
      </div>

      
      <div class="scene-panel" id="panel-1">
        <div class="modal-tag tag-could">COULD</div>
        <div class="scene-visual">
          <div class="avatar-icon">🚲</div>
          <span class="time-chip">Leo · Past Ability</span>
        </div>
      </div>
    </div>

    
    <div class="controls">
      <button class="dot active" onclick="setMode(0)" aria-label="Step 1"></button>
      <button class="dot" onclick="setMode(1)" aria-label="Step 2"></button>
    </div>
  </div>

  <script>
    let currentIndex = 0;
    let autoTimer = null;

    const panels = [document.getElementById('panel-0'), document.getElementById('panel-1')];
    const buttons = [document.getElementById('btn-now'), document.getElementById('btn-past')];
    const dots = document.querySelectorAll('.dot');

    function setMode(index, userAction = true) {
      if (userAction && autoTimer) {
        clearInterval(autoTimer);
        autoTimer = null;
      }
      currentIndex = index;
      panels.forEach((p, i) => p.classList.toggle('active', i === index));
      buttons.forEach((b, i) => b.classList.toggle('active', i === index));
      dots.forEach((d, i) => d.classList.toggle('active', i === index));
    }

    // Auto-advance calmly every 3.5 seconds
    autoTimer = setInterval(() => {
      currentIndex = (currentIndex + 1) % 2;
      setMode(currentIndex, false);
    }, 3500);
  </script>
</body>
</html>

What happens when you need to ask a teacher or parent for permission to do something?

## Expressing Permission: May, Can, and Could

You might hear friends say "Can I borrow a pencil?", but **may** is the formal and polite way to ask for **permission**.

Saying "Can I leave?" asks about your physical ability, while "May I leave?" asks if you are allowed to go.

You can also use **could** to make polite requests for permission, like saying, "Could I leave a few minutes early?"

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="aspect-ratio" content="4:3">
<style>
  * { box-sizing: border-box; margin: 0; padding: 0; }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    color: #1e2945;
    background: transparent;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    padding: 12px;
  }

  .nav-bar {
    display: flex;
    gap: 8px;
    margin-bottom: 16px;
    width: 100%;
    max-width: 480px;
    justify-content: center;
  }

  .tab-btn {
    flex: 1;
    padding: 10px 8px;
    border: 2px solid #e2e8f0;
    background: #ffffff;
    border-radius: 12px;
    font-size: 14px;
    font-weight: 600;
    color: #64748b;
    cursor: pointer;
    text-align: center;
    transition: all 0.25s ease;
    user-select: none;
    box-shadow: 0 1px 3px rgba(0,0,0,0.04);
  }

  .tab-btn.active {
    border-color: #22b7ff;
    background: #f0f9ff;
    color: #0284c7;
    box-shadow: 0 2px 8px rgba(34, 183, 255, 0.2);
  }

  .grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 12px;
    width: 100%;
    max-width: 480px;
  }

  .verb-card {
    background: #ffffff;
    border-radius: 14px;
    padding: 16px 12px;
    text-align: center;
    border: 2px solid #f1f5f9;
    box-shadow: 0 2px 6px rgba(0,0,0,0.04);
    transition: all 0.3s ease;
    position: relative;
    min-height: 120px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
  }

  .verb-card.active {
    border-color: #22b7ff;
    background: #ffffff;
    box-shadow: 0 4px 14px rgba(34, 183, 255, 0.18);
    transform: translateY(-2px);
  }

  .verb-card.inactive {
    opacity: 0.32;
    background: #f8fafc;
    border-color: #f1f5f9;
  }

  .verb-title {
    font-size: 20px;
    font-weight: 800;
    letter-spacing: 0.5px;
    color: #0f172a;
    margin-bottom: 6px;
  }

  .badge {
    font-size: 13px;
    font-weight: 600;
    padding: 4px 10px;
    border-radius: 20px;
    background: #e0f2fe;
    color: #0369a1;
    margin-bottom: 6px;
    display: inline-block;
  }

  .example {
    font-size: 13px;
    color: #475569;
    font-style: italic;
  }

  .status-tag {
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.6px;
    color: #94a3b8;
    margin-top: 4px;
  }

  .verb-card.active .status-tag {
    color: #0284c7;
  }
</style>
</head>
<body>

<div class="nav-bar">
  <button class="tab-btn active" data-role="permission">✋ Permission</button>
  <button class="tab-btn" data-role="possibility">🌤️ Possibility</button>
  <button class="tab-btn" data-role="ability">🏃 Ability</button>
</div>

<div class="grid">
  
  <div class="verb-card" id="card-can">
    <div class="verb-title">can</div>
    <div class="badge" id="badge-can">Casual</div>
    <div class="example" id="ex-can">"Can I go?"</div>
    <div class="status-tag" id="tag-can">Allowed</div>
  </div>

  
  <div class="verb-card" id="card-could">
    <div class="verb-title">could</div>
    <div class="badge" id="badge-could">Polite</div>
    <div class="example" id="ex-could">"Could I leave?"</div>
    <div class="status-tag" id="tag-could">Polite Ask</div>
  </div>

  
  <div class="verb-card" id="card-may">
    <div class="verb-title">may</div>
    <div class="badge" id="badge-may">Formal</div>
    <div class="example" id="ex-may">"You may enter."</div>
    <div class="status-tag" id="tag-may">Granted</div>
  </div>

  
  <div class="verb-card" id="card-might">
    <div class="verb-title">might</div>
    <div class="badge" id="badge-might">—</div>
    <div class="example" id="ex-might">—</div>
    <div class="status-tag" id="tag-might">Not used</div>
  </div>
</div>

<script>
  const data = {
    permission: {
      can:   { active: true,  badge: "Casual",  ex: '"Can I go?"',       tag: "Informal" },
      could: { active: true,  badge: "Polite",  ex: '"Could I leave?"',  tag: "Polite Request" },
      may:   { active: true,  badge: "Formal",  ex: '"You may enter."',  tag: "Granted" },
      might: { active: false, badge: "—",       ex: "—",                 tag: "Rare / Archaic" }
    },
    possibility: {
      can:   { active: false, badge: "—",       ex: "—",                 tag: "General Rule" },
      could: { active: true,  badge: "Maybe",   ex: '"It could snow."',  tag: "Possible" },
      may:   { active: true,  badge: "Likely",  ex: '"It may rain."',    tag: "Probable" },
      might: { active: true,  badge: "Unsure",  ex: '"It might storm."', tag: "Slight Chance" }
    },
    ability: {
      can:   { active: true,  badge: "Present", ex: '"I can swim."',     tag: "Able Now" },
      could: { active: true,  badge: "Past",    ex: '"I could run fast."', tag: "Past Ability" },
      may:   { active: false, badge: "—",       ex: "—",                 tag: "Not used" },
      might: { active: false, badge: "—",       ex: "—",                 tag: "Not used" }
    }
  };

  const verbs = ['can', 'could', 'may', 'might'];
  const tabs = document.querySelectorAll('.tab-btn');

  function setMode(mode) {
    tabs.forEach(tab => {
      tab.classList.toggle('active', tab.dataset.role === mode);
    });

    const info = data[mode];
    verbs.forEach(v => {
      const card = document.getElementById(`card-${v}`);
      const badge = document.getElementById(`badge-${v}`);
      const ex = document.getElementById(`ex-${v}`);
      const tag = document.getElementById(`tag-${v}`);
      const item = info[v];

      if (item.active) {
        card.className = 'verb-card active';
        badge.textContent = item.badge;
        badge.style.display = 'inline-block';
        ex.textContent = item.ex;
        ex.style.display = 'block';
        tag.textContent = item.tag;
      } else {
        card.className = 'verb-card inactive';
        badge.style.display = 'none';
        ex.style.display = 'none';
        tag.textContent = item.tag;
      }
    });
  }

  tabs.forEach(tab => {
    tab.addEventListener('click', () => {
      setMode(tab.dataset.role);
    });
  });

  setMode('permission');
</script>
</body>
</html>

What if you are not asking for permission, but guessing what the weather will do tomorrow?

## Expressing Possibility: May, Might, and Could

We use **may** and **might** when something is possible, but not 100 percent certain.

Before using these words in sentences, keep two essential grammar rules in mind.

Under the **Structural Invariance Rule**, modal verbs never conjugate for third-person singular subjects (never add *-s* or *-es*, like "He **can** swim", not "He cans swim") and never take *-ed* or *-ing* endings.

Under the **Base Form Rule**, the main verb following a modal auxiliary must always remain in its bare base form without *to* (e.g., "She **might join**", not "She might to join" or "She might joins").

Both words show a chance of happening, but **might** often suggests a slightly smaller chance than **may**.

**Could** also expresses present or future possibility (for example, "Take an umbrella; it could rain").

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="aspect-ratio" content="4:3">
<style>
  * { box-sizing: border-box; margin: 0; padding: 0; }
  body {
    font-family: system-ui, -apple-system, sans-serif;
    color: #1e2945;
    background: transparent;
    padding: 12px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100%;
  }

  .nav-tabs {
    display: flex;
    gap: 8px;
    margin-bottom: 14px;
    width: 100%;
    max-width: 440px;
    justify-content: center;
  }

  .tab-btn {
    flex: 1;
    padding: 8px 10px;
    font-size: 14px;
    font-weight: 600;
    border: 1px solid #e2e8f0;
    background: #ffffff;
    color: #64748b;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    text-align: center;
  }

  .tab-btn.active {
    background: #6366f1;
    color: #ffffff;
    border-color: #6366f1;
    box-shadow: 0 2px 8px rgba(99, 102, 241, 0.25);
  }

  .display-box {
    width: 100%;
    max-width: 440px;
    background: #ffffff;
    border: 1px solid #e2e8f0;
    border-radius: 12px;
    padding: 16px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.03);
  }

  .view-panel {
    display: none;
    flex-direction: column;
    gap: 12px;
  }

  .view-panel.active {
    display: flex;
  }

  .item-row {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 8px 12px;
    border-radius: 8px;
    background: #f8fafc;
    border: 1px solid #edf2f7;
    cursor: pointer;
    transition: background 0.2s ease, border-color 0.2s ease;
  }

  .item-row:hover, .item-row.selected {
    background: #f0f4ff;
    border-color: #c7d2fe;
  }

  .modal-badge {
    font-weight: 700;
    font-size: 15px;
    width: 64px;
    color: #4338ca;
  }

  .meter-bar {
    flex: 1;
    height: 12px;
    background: #e2e8f0;
    border-radius: 6px;
    overflow: hidden;
  }

  .meter-fill {
    height: 100%;
    border-radius: 6px;
    transition: width 0.4s ease;
  }

  .val-label {
    font-size: 13px;
    font-weight: 600;
    width: 86px;
    text-align: right;
    color: #64748b;
  }

  .fill-might { width: 30%; background: #f59e0b; }
  .fill-may   { width: 50%; background: #0ea5e9; }
  .fill-could { width: 65%; background: #6366f1; }
  .fill-can   { width: 95%; background: #10b981; }

  .polite-formal { width: 90%; background: #6366f1; }
  .polite-medium { width: 65%; background: #0ea5e9; }
  .polite-casual { width: 40%; background: #10b981; }

  .time-badge {
    padding: 3px 8px;
    border-radius: 6px;
    font-size: 12px;
    font-weight: 600;
  }
  .time-past { background: #fee2e2; color: #b91c1c; }
  .time-pres { background: #dcfce7; color: #15803d; }

  .visual-cue {
    font-size: 20px;
    line-height: 1;
    width: 24px;
    text-align: center;
  }
</style>
</head>
<body>

<div class="nav-tabs">
  <button class="tab-btn active" onclick="showTab(0)">Possibility</button>
  <button class="tab-btn" onclick="showTab(1)">Permission</button>
  <button class="tab-btn" onclick="showTab(2)">Ability</button>
</div>

<div class="display-box">
  
  <div class="view-panel active" id="view-0">
    <div class="item-row">
      <span class="visual-cue">🎲</span>
      <span class="modal-badge">Might</span>
      <div class="meter-bar"><div class="meter-fill fill-might"></div></div>
      <span class="val-label">Low</span>
    </div>
    <div class="item-row">
      <span class="visual-cue">⛅</span>
      <span class="modal-badge">May</span>
      <div class="meter-bar"><div class="meter-fill fill-may"></div></div>
      <span class="val-label">Medium</span>
    </div>
    <div class="item-row">
      <span class="visual-cue">💡</span>
      <span class="modal-badge">Could</span>
      <div class="meter-bar"><div class="meter-fill fill-could"></div></div>
      <span class="val-label">Possible</span>
    </div>
    <div class="item-row">
      <span class="visual-cue">☀️</span>
      <span class="modal-badge">Can</span>
      <div class="meter-bar"><div class="meter-fill fill-can"></div></div>
      <span class="val-label">General</span>
    </div>
  </div>

  
  <div class="view-panel" id="view-1">
    <div class="item-row">
      <span class="visual-cue">🎩</span>
      <span class="modal-badge">May</span>
      <div class="meter-bar"><div class="meter-fill polite-formal"></div></div>
      <span class="val-label">Formal</span>
    </div>
    <div class="item-row">
      <span class="visual-cue">🤝</span>
      <span class="modal-badge">Could</span>
      <div class="meter-bar"><div class="meter-fill polite-medium"></div></div>
      <span class="val-label">Polite</span>
    </div>
    <div class="item-row">
      <span class="visual-cue">👋</span>
      <span class="modal-badge">Can</span>
      <div class="meter-bar"><div class="meter-fill polite-casual"></div></div>
      <span class="val-label">Casual</span>
    </div>
  </div>

  
  <div class="view-panel" id="view-2">
    <div class="item-row">
      <span class="visual-cue">⚡</span>
      <span class="modal-badge">Can</span>
      <div class="meter-bar"><div class="meter-fill" style="width: 100%; background: #10b981;"></div></div>
      <span class="time-badge time-pres">Present</span>
    </div>
    <div class="item-row">
      <span class="visual-cue">🕰️</span>
      <span class="modal-badge">Could</span>
      <div class="meter-bar"><div class="meter-fill" style="width: 100%; background: #f59e0b;"></div></div>
      <span class="time-badge time-past">Past</span>
    </div>
  </div>
</div>

<script>
function showTab(idx) {
  const tabs = document.querySelectorAll('.tab-btn');
  const panels = document.querySelectorAll('.view-panel');
  tabs.forEach((tab, i) => tab.classList.toggle('active', i === idx));
  panels.forEach((panel, i) => panel.classList.toggle('active', i === idx));
}
</script>

</body>
</html>

According to the **Structural Invariance Rule**, modal verbs never change their form—never add **-s**, **-ed**, or **-ing** (say *He can swim*, never *He cans swim*).

Under the **Base Form Rule**, the main verb following a modal must always stay in its bare base form without *to* (say *She might join*, not *She might to join*).

Ready to test your detective skills and pick the perfect helper verb for every sentence?

Look at the clue in each sentence to choose the exact right modal auxiliary verb.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="aspect-ratio" content="4:3">
<style>
  * { box-sizing: border-box; margin: 0; padding: 0; }
  body {
    font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: transparent;
    color: #1e2945;
    padding: 12px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 100%;
    user-select: none;
  }

  .nav-tabs {
    display: flex;
    gap: 8px;
    width: 100%;
    max-width: 480px;
    margin-bottom: 12px;
  }

  .tab-btn {
    flex: 1;
    border: none;
    background: #f1f5f9;
    color: #64748b;
    font-size: 15px;
    font-weight: 700;
    padding: 10px 4px;
    border-radius: 10px;
    cursor: pointer;
    box-shadow: 0 0 0 2px rgba(0,0,0,0);
    transition: background 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
    text-align: center;
  }

  .tab-btn.active {
    background: #ffffff;
    color: #0284c7;
    box-shadow: 0 0 0 2px #0284c7, 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  }

  .display-card {
    background: #ffffff;
    border: 1px solid #e2e8f0;
    border-radius: 16px;
    padding: 18px 16px;
    width: 100%;
    max-width: 480px;
    display: flex;
    flex-direction: column;
    gap: 16px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.05);
  }

  .meaning-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 8px;
  }

  .tag-badge {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    background: #f0fdf4;
    color: #15803d;
    border-radius: 20px;
    padding: 6px 14px;
    font-size: 14px;
    font-weight: 700;
    box-shadow: 0 0 0 1px #bbf7d0;
  }

  .time-badge {
    background: #f8fafc;
    color: #475569;
    border-radius: 20px;
    padding: 6px 12px;
    font-size: 13px;
    font-weight: 600;
    box-shadow: 0 0 0 1px #e2e8f0;
  }

  .meter-container {
    display: flex;
    flex-direction: column;
    gap: 6px;
  }

  .meter-label-row {
    display: flex;
    justify-content: space-between;
    font-size: 12px;
    font-weight: 600;
    color: #64748b;
  }

  .meter-bar {
    height: 12px;
    background: #e2e8f0;
    border-radius: 6px;
    overflow: hidden;
    position: relative;
  }

  .meter-fill {
    height: 100%;
    width: 100%;
    background: #0284c7;
    border-radius: 6px;
    transition: width 0.4s ease, background-color 0.4s ease;
  }

  .visual-box {
    display: flex;
    align-items: center;
    justify-content: center;
    background: #f8fafc;
    border: 1px dashed #cbd5e1;
    border-radius: 12px;
    padding: 16px;
    gap: 12px;
    font-size: 28px;
  }

  .sentence-text {
    font-size: 16px;
    font-weight: 600;
    color: #1e2945;
  }

  .highlight {
    color: #0284c7;
    text-decoration: underline;
    font-weight: 800;
  }
</style>
</head>
<body>

<div class="nav-tabs" role="tablist">
  <button class="tab-btn active" onclick="showModal('can')">can</button>
  <button class="tab-btn" onclick="showModal('could')">could</button>
  <button class="tab-btn" onclick="showModal('may')">may</button>
  <button class="tab-btn" onclick="showModal('might')">might</button>
</div>

<div class="display-card">
  <div class="meaning-row">
    <div id="functionBadge" class="tag-badge">
      <span id="roleIcon">💪</span>
      <span id="roleLabel">Ability</span>
    </div>
    <div id="timeBadge" class="time-badge">Present ⏱️</div>
  </div>

  <div class="meter-container">
    <div class="meter-label-row">
      <span>Certainty</span>
      <span id="percentLabel">100%</span>
    </div>
    <div class="meter-bar">
      <div id="meterFill" class="meter-fill" style="width: 100%;"></div>
    </div>
  </div>

  <div class="visual-box">
    <span id="visualIcon">🏊</span>
    <span class="sentence-text" id="sentenceBox">I <span class="highlight">can</span> swim.</span>
  </div>
</div>

<script>
  const data = {
    can: {
      role: 'Ability',
      icon: '💪',
      time: 'Present ⏱️',
      certainty: '100%',
      width: '100%',
      color: '#10b981',
      vIcon: '🏊',
      sentence: 'I <span class="highlight" style="color:#10b981">can</span> swim.'
    },
    could: {
      role: 'Past Ability',
      icon: '⏳',
      time: 'Past ⏪',
      certainty: '80%',
      width: '80%',
      color: '#3b82f6',
      vIcon: '🏃',
      sentence: 'I <span class="highlight" style="color:#3b82f6">could</span> run fast.'
    },
    may: {
      role: 'Permission',
      icon: '🔑',
      time: 'Present / Future ⏱️',
      certainty: '50%',
      width: '50%',
      color: '#8b5cf6',
      vIcon: '🚪',
      sentence: 'You <span class="highlight" style="color:#8b5cf6">may</span> enter.'
    },
    might: {
      role: 'Possibility',
      icon: '🎲',
      time: 'Uncertain ❓',
      certainty: '25%',
      width: '25%',
      color: '#f59e0b',
      vIcon: '🌧️',
      sentence: 'It <span class="highlight" style="color:#f59e0b">might</span> rain.'
    }
  };

  const buttons = document.querySelectorAll('.tab-btn');
  const roleLabel = document.getElementById('roleLabel');
  const roleIcon = document.getElementById('roleIcon');
  const timeBadge = document.getElementById('timeBadge');
  const percentLabel = document.getElementById('percentLabel');
  const meterFill = document.getElementById('meterFill');
  const visualIcon = document.getElementById('visualIcon');
  const sentenceBox = document.getElementById('sentenceBox');

  function showModal(key) {
    buttons.forEach(btn => {
      btn.classList.toggle('active', btn.textContent.trim().toLowerCase() === key);
    });

    const item = data[key];
    roleLabel.textContent = item.role;
    roleIcon.textContent = item.icon;
    timeBadge.textContent = item.time;
    percentLabel.textContent = item.certainty;
    meterFill.style.width = item.width;
    meterFill.style.backgroundColor = item.color;
    visualIcon.textContent = item.vIcon;
    sentenceBox.innerHTML = item.sentence;
  }
</script>

</body>
</html>

Next time you speak or write, pause and ask yourself: am I talking about what I **can** do, what I **may** do, or what **might** happen next?

Using Modal Auxiliaries: Can, Could, May, and Might. Use can, could, may, and might to express ability, possibility, and permission.

Modal Verbs: The Parts of Speech (Grammar)

Use the Correct Modal Verb (Grade 4 Language Arts - Skill PP.5)

6 Minute Grammar: Modals of Possibility and Ability (Can, Could, May, Might)

Effective instruction for 4th graders on CCSS L.4.1.c centers on connecting modal auxiliaries to concrete real-world contexts. Teachers should use scenario-based sorting games (e.g., 'Skill vs. Permission vs. Guess') where students categorize sentences based on intent. Emphasize the 'helping verb + base verb' formula ($	ext{Modal} + 	ext{Base Verb}$) through choral response and sentence manipulation strips, ensuring students avoid inflectional traps like adding '-s' or 'to' after modals.

Using Modal Auxiliaries: Can, Could, May, and Might

Expressing Ability: Can and Could

Expressing Permission: May, Can, and Could