def count_words(sentence):
    counts = {}
    start = 0
    for i, ch in enumerate(sentence + " "):
        if not (ch.isalnum() or ch == "'"):
            word = sentence[start:i].lower().strip("'")
            start = i + 1
            if word:
                counts[word] = counts.get(word, 0) + 1

    return counts